problem upgrading with playerprefs.

I have a racing game and I'm trying to make upgrades. once you beat a level you haven't beat before, it gives you an upgrade point you can use to increase your speed or handling. the problem is that it gives me a point like normal when I win, but it gets set to zero when I go back to the start menu. keep in mind that both my level scene and my level select scene use the same code I used two codes for this so it might be very complicated.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class WinLevel : MonoBehaviour {
 
     public Text WinText;
     public Button WinButton;
     public Text ButtonText;
     public string LevelUnlocked = "Level2";
     public int LevelToUnlock = 2;
     int LevelReached = PlayerPrefs.GetInt("LevelReached");
     public int UpgradePoints = PlayerPrefs.GetInt("UpgradePoints");
     public Button[] levelButtons;
     public Text[] levelTexts;
     public Text[] ButtonTexts;
     private bool IsFinished = false;
 
     // Use this for initialization
     void Start()
     {
         LevelReached = PlayerPrefs.GetInt("LevelReached");
 
         UpgradePoints = PlayerPrefs.GetInt("UpgradePoints");
 
         Debug.Log("Points: " + UpgradePoints);
 
         for (int i = 0; i < levelButtons.Length; i++)
         {
             LevelReached = PlayerPrefs.GetInt("LevelReached");
 
             if (i + 1 > LevelReached)
             {
                 levelButtons[i].enabled = false;
                 levelTexts[i].enabled = false;
                 ButtonTexts[i].enabled = false;
             }
         }
         Debug.Log("LevelReached is " + LevelReached);
         Debug.Log("LevelToUnlock is " + LevelToUnlock);
     }
 
     void OnTriggerEnter(Collider other)
     {
         if (other.CompareTag("FinishLine"))
         {
             WinText.enabled = true;
             WinButton.enabled = true;
             ButtonText.enabled = true;
 
             if ( LevelToUnlock > LevelReached && !IsFinished)
             {
                 PlayerPrefs.SetInt("LevelReached", LevelToUnlock);
                 Debug.Log("Level Unlocked!");
                 PlayerPrefs.SetInt("UpgradePoints", UpgradePoints++);
                 Debug.Log("Points: " + UpgradePoints);
             }
             IsFinished = true;
         }
     }
     private void Update()
     {
         
     }
 }
 

as well as that code, I'm also using this code for using the upgrades

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class Upgrades : MonoBehaviour {
 
     public int UpgradePoints = PlayerPrefs.GetInt("UpgradePoints");
     public int Speed = PlayerPrefs.GetInt("Speed", -400);
     public int Handling = PlayerPrefs.GetInt("Handling");
     public int TurnSpeed = PlayerPrefs.GetInt("TurnSpeed");
     public int Boosts = PlayerPrefs.GetInt("Boosts");
 
     public Text PointsText;
     public AudioSource Sound;
 
     // Use this for initialization
     void Start () {
 
         UpgradePoints = PlayerPrefs.GetInt("UpgradePoints");
         Speed = PlayerPrefs.GetInt("Speed");
         TurnSpeed = PlayerPrefs.GetInt("TurnSpeed");
         PointsText.text = "Points: " + UpgradePoints;
         Debug.Log("Points: " + UpgradePoints);
     }
     
     // Update is called once per frame
     void Update () {
         UpgradePoints = PlayerPrefs.GetInt("UpgradePoints");
     }
 
     public void SpeedUpgrade(int su)
     {
         if (UpgradePoints > 0)
         {
             Sound.Play();
             PlayerPrefs.SetInt("Speed", Speed - 50);
             PlayerPrefs.SetInt("UpgradePoints", UpgradePoints--);
             UpgradePoints = UpgradePoints--;
             PointsText.text = "Points: " + UpgradePoints;
             Speed = PlayerPrefs.GetInt("Speed");
             Debug.Log("Speed: " + Speed);
         }
     }
 
     public void HandlingUpgrade(int hu)
     {
         if (UpgradePoints > 0)
         {
             PlayerPrefs.SetInt("UpgradePoints", UpgradePoints--);
             PointsText.text = "Points: " + UpgradePoints;
             Sound.Play();
         }
     }
 
     public void TurnSpeedUpgrade(int tu)
     {
         if (UpgradePoints > 0)
         {
             PlayerPrefs.SetInt("UpgradePoints", UpgradePoints--);
             PointsText.text = "Points: " + UpgradePoints;
             PlayerPrefs.SetInt("TurnSpeed", TurnSpeed + 5);
             TurnSpeed = PlayerPrefs.GetInt("TurnSpeed");
             Sound.Play();
             Debug.Log("TurnSpeed: " + TurnSpeed);
         }
     }
 
     public void BoostUpgrade(int bu)
     {
         if (UpgradePoints > 0)
         {
             PlayerPrefs.SetInt("UpgradePoints", UpgradePoints--);
             PointsText.text = "Points: " + UpgradePoints;
             Sound.Play();
         }
     }
 }
 

don't mind all that other stuff. I'm just focusing on the playerprefs when I start a scene. what here might cause a playerpref to go back to zero when the scene is loaded?