Why do objects keep spawning on top of one another?

I have made a game where some spikes are spawned on the side of the screen and above the side of the screen in random places. The problem is that they spawn on top of each other. I have tried to use the Physics2D.OverlapAreaAll, but it won't work. Here is code:

 void Start()
     { 
         cameraPos = Camera.main.transform.position;
         xValue.x = cameraPos.x + screenSize.x;
         screenSize.x = Vector2.Distance(Camera.main.ScreenToWorldPoint(new Vector2(0, 0)), Camera.main.ScreenToWorldPoint(new Vector2(Screen.width, 0))) * 0.5f; 
         screenSize.y = Vector2.Distance(Camera.main.ScreenToWorldPoint(new Vector2(0, 0)), Camera.main.ScreenToWorldPoint(new Vector2(0, Screen.height))) * 0.5f;
         Debug.Log(spawnPositions);
         InvokeRepeating("spawnTwoSpike", 1.0f, 1.0f);
     }
 
     private void spawnTwoSpike () 
     {
         Vector3 randomPositionX = getValidSpawnLocation(twoSpikes);
         Instantiate(twoSpikes, randomPositionX, Quaternion.identity);
         Instantiate(twoSpikesLeft, spawnPositionLeft, Quaternion.identity);
     }
 
     private void FixedUpdate()
     {
         cameraPos = Camera.main.transform.position;
         yValue.y = cameraPos.y + screenSize.y;
         maxY.y = yValue.y + 10;
         spawnPositions = new Vector2(xValue.x + (screenSize.x * 2) * 0.5f, Random.Range(yValue.y + (screenSize.y * 2) * .5f, (yValue.y + (screenSize.y * 2) * .5f) + 10));
         spawnPositionLeft = new Vector2(xValue.x - (screenSize.x * 2) * 0.5f, Random.Range(yValue.y + (screenSize.y * 2) * .5f, (yValue.y + (screenSize.y * 2) * .5f) + 10));
         Debug.Log(spawnPositions); 
     }
 
     private Vector3 getValidSpawnLocation(GameObject go)
     {
         // get the spawning object's collider to use for size
         Collider2D objectCollider = go.GetComponent<Collider2D>();
 
         Vector3 newPosition = Vector3.zero;
         bool validPosition = false;
         int failureLimit = 100;
         int fails = 0;
         do
         {
             // get a random position on screen
             newPosition = spawnPositions;
 
             // get the corners of the object at the new position
             Vector3 min = new Vector3(newPosition.x, newPosition.y - objectCollider.bounds.extents.y, newPosition.z);
             Vector3 max = new Vector3(newPosition.x, newPosition.y + objectCollider.bounds.extents.y, newPosition.z);
 
             // check that area for overlaps with the layermask
             Collider2D[] overlapObjects = Physics2D.OverlapAreaAll(min, max, doNotSpawnOnMe);
 
             // if it does not overlap any objects in the layermask
             if (overlapObjects.Length == 0)
             {
                 // break out of the do while loop
                 validPosition = true;
                 fails = 0;
             }
             else
             {
                 fails++;
             }
         } while (!validPosition && fails < failureLimit);
 
         // return the valid position
         return newPosition;
     }
    
 }