how do i keep repeating code till conditions are met so that the next part of the code can happen?

my code here is supposed to instantiate a cube randomly 1 unit left right up or down. but the spawn position (asteroidcore) keeps moving to already occupied spaces. i tryed to write code that would randomly move the spawnpos till there was nothing in its collider space and then it would instantiate a cube. but it doesnt work

 IEnumerator keepgeneratingasteroid()
     {
         GameObject lastasteroid;
         GameObject[] allasteroids = GameObject.FindGameObjectsWithTag("asteroid");
         lastasteroid = allasteroids[allasteroids.Length-1];
 
         
         while (true)
         {
             yield return new WaitForSeconds(.2f);
 
             xminus1thru1 = Random.Range(-1, 1);
             yminus1thru1 = Random.Range(-1, 1);
 
             if (xminus1thru1 != 0)
             {
                 yminus1thru1 = 0;
             }
             else if (yminus1thru1 != 0)
             {
                 xminus1thru1 = 0;
             }
 
             asteroidcollider = Physics2D.OverlapBoxAll(asteroidcore.transform.position, new Vector2(1, 1), 0);
 
             if (asteroidcollider.Length > 0)
             {
                 repositioncore();
                 asteroidcollider = Physics2D.OverlapBoxAll(asteroidcore.transform.position, new Vector2(1, 1), 0);
             }
             
             Instantiate(asteroid, asteroidcore.transform.position, new Quaternion(0, 0, 0, 0));
         }
 
         void repositioncore()
         {
             xminus1thru1 = Random.Range(-1, 1);
             yminus1thru1 = Random.Range(-1, 1);
             if (xminus1thru1 != 0)
             {
                 yminus1thru1 = 0;
             }
             else if (yminus1thru1 != 0)
             {
                 xminus1thru1 = 0;
             }
 
 
             Vector3 lastasteroidoffset = new Vector3(lastasteroid.transform.position.x + xminus1thru1, lastasteroid.transform.position.y + yminus1thru1, 0);
 
             asteroidcore.transform.position = lastasteroidoffset;
 
             asteroidcollider = Physics2D.OverlapBoxAll(asteroidcore.transform.position, new Vector2(1, 1), 0);
 
             Debug.Log("collider more than 0");
         }
 
           
     }