Instantiate Random 3D Objects/platforms that dont overlap

I am trying to instantiate 3 different prefab object platforms at random. These platforms have box colliders and rigid bodies ( is kinematic) attached to them. When they are instantiated their x and y positions are also random. These plat forms also move up/down or left/right. I am trying to figure out how to get them so they don't instantiate on top of each other and so when they move, don't collide/pass through the other platforms. Rigid body(with gravity) players land on the platforms,so I dont want them to fall through the platforms.

I am thinking that one would need to check the previously made platform x and then if the new randomly generated x is the same, randomly generate a new x, or something like this, though I am not sure how to do this with my code.

I am new to programming so please be specific in your answers (ie. If I need to add a line of code or take out a part please tell me exactly what to do) Any help would be greatly appreciated.

 public class cEndless : MonoBehaviour {
 
     public Transform player;
     public float playerHeightY;
     
     public Transform PlatAA;
     public Transform PlatAB;
     public Transform PlatAC;
     
     private int platNum; 
 
     public int currentNumPlat; //Self-explained
     public int maxNumPlat; //Self-explained
     
     // Use this for initialization
     void Start () {
         player = GameObject.FindGameObjectWithTag("Player").transform;    
         currentNumPlat = 0;
         maxNumPlat = 3;
 
         if (currentNumPlat == 0)
         {            
             Vector2 posAB = new Vector2(0,0);             
             Instantiate (PlatAA, posAB, Quaternion.identity);
             currentNumPlat += 1;
         }
     }    
     // Update is called once per frame
     void Update () {
         
         playerHeightY = player.position.y;
         
         if (currentNumPlat < maxNumPlat)
         {
             PlatformSpawner();            
         }    
     }
         
     void PlatformSpawner()
     {
         if (currentNumPlat < maxNumPlat) 
         {
             platNum = Random.Range(1,4);
             float x = Random.Range (-8, 8);
             float y = Random.Range (playerHeightY + 1.3f, playerHeightY +3.3f);
             Vector2 posXY = new Vector2 (x, y);
         
             
             if (platNum == 1) 
             {
                 Instantiate (PlatAA, posXY, Quaternion.identity);
             }
             if (platNum == 2) 
             {
                 Instantiate (PlatAB, posXY, Quaternion.identity);
             }
             if (platNum == 3) 
             {
                 Instantiate (PlatAC, posXY, Quaternion.identity);
             }
 
             currentNumPlat += 1;
         }
     }
 }