Stack Problem(Please help!)

I have an inventory script on the player an an object with the itemdatabase. I create a label on each item with the stackamount of the item. I store the amount in each item and update it for each of them but when I have two items with the same id instead of creating a new one with 1 stackAmount it creates one that has an amount linked to the first item. Like if I change the stackAmount it changes for both of them.

InventoryScript:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class Inventory : MonoBehaviour
 {
     public int slotsX, slotsY;
     public GUISkin skin;
     public List<Item> inventory = new List<Item>();
     public List<Item> slots = new List<Item>();
     public bool showInventory;
     private ItemDatabase database;
     private bool showTooltip;
     private string tooltip;
 
     public bool usingItem;
     int lastBlockUsed;
 
     private bool draggingItem;
     private Item draggedItem;
     private int previousIndex;
 
     float screenRatio;
     Vector2 ScaleOnRatio = new Vector2(0.1f, 0.1f);
     GameObject player;
 
 
     void Start()
     {
         database = GameObject.FindGameObjectWithTag("ItemDatabase").GetComponent<ItemDatabase>();
         player = GameObject.FindGameObjectWithTag("Player");
 
         for (int i = 0; i < (slotsX * slotsY); i++) 
         {
             slots.Add(new Item());
             inventory.Add(new Item());
         }
 
         AddItem(0);
         AddItem(0);
         AddItem(0);
         AddItem(0);
         AddItem(1);
         AddItem(1);
     }
 
     void Update()
     {
         screenRatio = Screen.width / Screen.height;
                
         if (Input.GetKeyDown(KeyCode.E))
         {
             showInventory = !showInventory;
         }
         if (player.GetComponent<Player>().BlockPlaced == true)
         {
             showInventory = true;
             player.GetComponent<Player>().BlockPlaced = false;
         }
     }
 
     void OnGUI()
     {
         tooltip = "";
         GUI.skin = skin;
 
         if (usingItem && Input.GetKeyDown(KeyCode.E))
         {
             AddItem(lastBlockUsed);
             GameObject.FindGameObjectWithTag("Player").GetComponent<Player>().PrefabBlock = null;
             usingItem = false;
         }
 
         if (showInventory)
         {
             DrawInventory();
         }
 
         if (showTooltip && showInventory)
             GUI.Box(new Rect(Event.current.mousePosition.x, Event.current.mousePosition.y, 200, 200), tooltip, skin.GetStyle("Tooltip"));
 
         if (draggingItem)
             GUI.DrawTexture(new Rect(Event.current.mousePosition.x, Event.current.mousePosition.y, 50, 50), draggedItem.itemIcon);
         
     }
 
     void DrawInventory()
     {
         Event e = Event.current;
 
         int i = 0;
         for (int y = 0; y < slotsX; y++)
         {
             for (int x = 0; x < slotsY; x++)
             {
                 Rect slotRect = new Rect(x * 70, y * 70, 700 * ScaleOnRatio.x, 700 * (screenRatio * ScaleOnRatio.y));
 
                 GUI.Box(new Rect(slotRect), "", skin.GetStyle("Slot"));
                 
                 slots[i] = inventory[i];
 
                 if (slots[i].itemName != null)
                 {
                     GUI.DrawTexture(slotRect, slots[i].itemIcon);
 
                     if(slots[i].itemAmount > 1)
                     GUI.Label(slotRect, "" + slots[i].itemAmount, skin.GetStyle("Stack"));
 
                     if (slotRect.Contains(e.mousePosition))
                     {
                         if (!draggingItem)
                         {
                             CreateTooltip(slots[i]);
                             showTooltip = true;
                         }
 
                         if (e.button == 0 && e.type == EventType.MouseDrag && !draggingItem)
                         {
                             draggingItem = true;
                             previousIndex = i;
                             draggedItem = slots[i];
                             inventory[i] = new Item();
                         }
                         if (e.type == EventType.MouseUp && draggingItem)
                         {
                             inventory[previousIndex] = inventory[i];
                             inventory[i] = draggedItem;
                             draggingItem = false;
                             draggedItem = null;
                         }
 
                         if (e.isMouse && e.type == EventType.MouseDown && e.button == 1)
                         {
                             if (slots[i].itemType == Item.ItemType.Block || slots[i].itemType == Item.ItemType.Trap)
                             {
                                 UseItem(slots[i], i, true);
                             }
                         }
                     }
                 }
                 else
                 {
                     if (slotRect.Contains(e.mousePosition))
                     {
                         if(e.type == EventType.MouseUp && draggingItem)
                         {
                             inventory[previousIndex] = inventory[i];
                             inventory[i] = draggedItem;
                             draggingItem = false;
                             draggedItem = null;
                         }
                     }
                 }
 
                 if (tooltip == "")
                 {
                     showTooltip = false;
                 }
                 i++;
             }
         }
     }
 
     string CreateTooltip(Item item)
     {
         if (item.itemType == Item.ItemType.Trap)
             tooltip = "<color=#b85035>" + item.itemName + "</color>";
         else
         tooltip = item.itemName;
 
         return tooltip;
     }
 
     void UseItem(Item item, int slot, bool deleteItem)
     {
         usingItem = true;
         lastBlockUsed = item.itemID;
 
         GameObject.FindGameObjectWithTag("Player").GetComponent<Player>().PrefabBlock = Resources.Load<GameObject>("PrefabBlock/" + item.itemName);
 
         if (deleteItem && item.itemAmount <= 1)
         {
             inventory[slot] = new Item();
         }
         else if (deleteItem && item.itemAmount > 1)
         {
             item.itemAmount -= 1;
         }
 
         if (player.GetComponent<Player>().BuildMode == true && player.GetComponent<Player>().BlockPlaced == false)
             showInventory = false;
 
 
         showTooltip = false;
     }
 
     void RemoveItem(int id)
     {
         for (int i = 0; i < inventory.Count; i++)
         {
             if(inventory[i].itemID == id)
             {
                 inventory[i] = new Item();
                 break;
             }
         }
     }
 
     public void AddItem(int id)
     {
 
         for (int i = 0; i < inventory.Count; i++)
         {
             if (inventory[i].itemAmount == inventory[i].stackMax || inventory[i].itemName == null)
             {
                 for (int j = 0; j < database.items.Count; j++)
                 {
                     if (database.items[j].itemID == id)
                     {
                         inventory[i] = database.items[j];
                     }
                 }
                 break;
             }
 
             if (ItemInInventory(inventory[i], id) && inventory[i].itemAmount < inventory[i].stackMax)
             {
                 if (inventory[i].itemID == id)
                 {
                     slots[i].itemAmount += 1;
                     break;
                 }
             }
         }
     }
 
     bool InventoryContains(int id)
     {
         bool result = false;
         for (int i = 0; i < inventory.Count; i++) 
         {
             result = inventory[i].itemID == id;
             if (result)
             {
                 break;
             }
         }
         return result;
     }
 
     bool ItemInInventory(Item item, int id)
     {
         for (int i = 0; i < inventory.Count; i++)
         {
             if (inventory[i].itemID == item.itemID)
                 return true;
         }
         return false;
     }
 }
 
 
 
 

Item Database:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class ItemDatabase : MonoBehaviour
 {
     public List<Item> items = new List<Item>();
 
     void Start()
     {
         items.Add(new Item("SpikeTrap", 0, "A spike that appears from the ground ", 1, 0, Item.ItemType.Trap, 16));
         items.Add(new Item("WoodFloor", 1, "a ", 1, 0, Item.ItemType.Block, 16));
         items.Add(new Item("WoodFloor", 1, "a ", 1, 0, Item.ItemType.Block, 16));
     }
 }

ItemCreateScript:

 using System.Collections;
 using UnityEngine;
 
 [System.Serializable]
 public class Item
 {
     public string itemName;
     public int itemID;
     public string itemDesc;
     public Texture2D itemIcon;
     public int itemAmount;
     public int itemSpeed;
     public ItemType itemType;
     public int stackMax;
 
 
     public enum ItemType
     {
         Weapon,
         Trap,
         Monster,
         Block
     }
 
     public Item(string name, int id, string desc, int amount, int speed, ItemType type, int stackmax)
     {
         itemName = name;
         itemID = id;
         itemDesc = desc;
         itemIcon = Resources.Load<Texture2D>("Icons/" + name + "Icon");
         itemAmount = amount;
         itemSpeed = speed;
         itemType = type;
         stackMax = stackmax;
 
     }
     public Item()
     {
         itemID = -1;
     }
 }