How to spawn a prefab every 5 second randomly between a set range?

I'm struggling to spawn a prefab in without it being a gameobject, and I want it one to spawn in every 5 seconds between a set range? any help would be appreciated!

public class obstacle : MonoBehaviour {

 private Rigidbody2D rb2d;
 private float obstacleSpawnCounter;
 public Vector3 spawnPosition;
 public GameObject spike;

 // Use this for initialization
 void Start () {

     rb2d = GetComponent<Rigidbody2D>();
     rb2d.isKinematic = true;
     GetComponent<SpriteRenderer>().sortingOrder = 4;

 }
 
 // Update is called once per frame
 void Update () {
     if (Input.GetMouseButtonDown(0))
     {
         if (rb2d.isKinematic)
             rb2d.isKinematic = false;
     }
     obstacleSpawnCounter += Time.deltaTime;
     if (obstacleSpawnCounter > 5)
     {
         SpawnObstacle();
         obstacleSpawnCounter -= 5;
     }
     this.transform.Translate(0, 0.06f, 0);
 }

 public void SpawnObstacle()
 {
     Instantiate(spike, spawnPosition, Quaternion.identity);
 }

}