Instantiate Prefab at random times but keep 3 from spawning

I'm having an issue with one of my scripts. What I'm trying to do is instantiate my enemy prefab at random times and I had success in that.

My only problem is that I want it to spawn at random but I don't want the spawn points to spawn 3 in a row like you can see above. Here is my spawning script:

 using UnityEngine;
 using System.Collections;
 
 public class spawnEnemy : MonoBehaviour {
     public float time = 1.0F;
     float realTime;
     public GameObject enemy;
     Random rnd = new Random();
     public bool instancedPrefab = false;
     // Use this for initialization
     void Start () {
         realTime = time;
         StartCoroutine(enemySpawn());
         StartCoroutine(timeChanger());
     }
     
     // Update is called once per frame
     void Update () {
         //GameObject.Instantiate(enemy);
     }
 
     IEnumerator enemySpawn()
     {
         while(true)
         {
             yield return new WaitForSeconds(realTime);
             enemy.transform.position = this.gameObject.transform.position;
             Instantiate(enemy);
         }
     }
     IEnumerator timeChanger()
     {
         while(true)
         {
             yield return new WaitForSeconds(2);
             int randFirst = Random.Range(1, 3);
             int randSeccond = Random.Range(4, 6);
             int randNumber = Random.Range(randFirst, randSeccond);
             realTime = randNumber;
         }
     }
 }