Custom Inspector resets after Unity restarts

Hello Everybody,

I made a simple custom Inspector editor script for my weapon pick up script that I use to pick up all of my weapons in-game, but recently I ran into one issue. I noticed that everytime I play the game the changed variables would reset. I searched the internet for answers and I found one that worked. It was by using 'EditorUtility.SetDirty'. But this didn't solve the problem, not really anyway, because everytime I close the Unity and I open it again the changed variables would still reset. I did the same thing I looked in the internet for answers, but this time I couldn't find anything that would actually work..
Can anyone help me with this? Thank you!

The Editor Script:

 using UnityEditor;
 using UnityEngine;
 
 [CustomEditor(typeof(WeaponPickUp))]
 public class WeaponPickUp_PropertyHolderEditor : Editor
 {
     public WeaponPickUp weaponPickUp;
 
     void OnEnable ()
     {
         weaponPickUp = (WeaponPickUp)target;
     }
 
     public override void OnInspectorGUI ()
     {
         EditorGUILayout.Space();
         EditorGUILayout.LabelField("Assign Weapon Item", EditorStyles.boldLabel);
         weaponPickUp.item = (Item)EditorGUILayout.ObjectField(weaponPickUp.item, typeof(Item), allowSceneObjects: true);
 
         EditorGUILayout.Space();
         EditorGUILayout.LabelField("Weapon Type", EditorStyles.boldLabel);
         weaponPickUp.weaponType = (Weapons.weaponType)EditorGUILayout.EnumPopup(weaponPickUp.weaponType);
 
         if (weaponPickUp.weaponType == Weapons.weaponType.Gun)
         {
             EditorGUILayout.Space();
             EditorGUILayout.LabelField("Choose Ammo Type", EditorStyles.boldLabel);
             weaponPickUp.Ammo_Type = (Bullets.Type)EditorGUILayout.EnumPopup("Ammo Type", weaponPickUp.Ammo_Type);
             EditorGUILayout.Space();
 
             int max = 0;
             switch (weaponPickUp.Ammo_Type)
             {
                 case Bullets.Type.AK47:
                     max = ValuesManager.maxAK47Ammo;
                     break;
                 case Bullets.Type.MP5:
                     max = ValuesManager.maxMP5Ammo;
                     break;
                 case Bullets.Type.M1911:
                     max = ValuesManager.maxHandGunAmmo;
                     break;
                 case Bullets.Type.Sniper:
                     max = ValuesManager.maxSniperAmmo;
                     break;
             }
 
             EditorGUILayout.LabelField("Add Amount", EditorStyles.boldLabel);
             weaponPickUp.Add_Amount = EditorGUILayout.IntSlider(weaponPickUp.Add_Amount, 1, max);
             EditorGUILayout.Space();
         }
 
         EditorGUILayout.LabelField("Assign Pick Up(-s) SFX", EditorStyles.boldLabel);
         weaponPickUp.weaponClip = (AudioClip)EditorGUILayout.ObjectField("Weapon clip: ", weaponPickUp.weaponClip, typeof(AudioClip), allowSceneObjects: true);
         if (weaponPickUp.weaponType == Weapons.weaponType.Gun)
         {
             weaponPickUp.ammoClip = (AudioClip)EditorGUILayout.ObjectField("Ammo clip: ", weaponPickUp.ammoClip, typeof(AudioClip), allowSceneObjects: true);
         }
         EditorGUILayout.Space();
 
         EditorGUILayout.LabelField("Sound Setting", EditorStyles.boldLabel);
         weaponPickUp._volume = EditorGUILayout.FloatField("Volume: ", weaponPickUp._volume);
         weaponPickUp._pitch = EditorGUILayout.FloatField("Pitch: ", weaponPickUp._pitch);
         weaponPickUp._randomizeValues = EditorGUILayout.Toggle("Randomize Settings: ", weaponPickUp._randomizeValues);
         EditorGUILayout.Space();
 
         if (GUI.changed) { EditorUtility.SetDirty(weaponPickUp); }
     }
 }