Help with AdMob interstitials

Hi guys I am looking for someone who can help me with this problem: I have this code

 private const string AD_UNIT_ID = "***********";
     private const string INTERSTITIAL_ID = "**********";
     private AdMobPlugin admob;
 
 
     public bool hidden = true;
 
 
     void Awake(){
         DontDestroyOnLoad (this);
     }
     // Use this for initialization
     void Start () {
         admob = GetComponent<AdMobPlugin> ();
         admob.CreateBanner (AD_UNIT_ID, AdMobPlugin.AdSize.SMART_BANNER, false, INTERSTITIAL_ID);
         admob.RequestAd ();
         admob.HideBanner ();
         admob.RequestInterstitial ();
     
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     public void BannerS(){
             admob.ShowBanner();
             hidden = false;
     }
 
     public void OnEnable(){
         AdMobPlugin.InterstitialLoaded += HandleInterstitialLoaded;
     }
 
     public void OnDisable(){
         AdMobPlugin.InterstitialLoaded -= HandleInterstitialLoaded;
     }
 
     public void HandleInterstitialLoaded ()
     {
         admob.ShowInterstitial ();
     }
 
     public void OnIntClosed(){
         AdMobPlugin.InterstitialClosed += OnAdClosed;
     }
     public void OnAdClosed(){
         admob.RequestAd ();
     }

So my question is: in my game the interstitial ad displays just once, how do I make interstitials show up when I tell them to? For example I have this IEnumerator which I call when something is pressed:

 IEnumerator WaitForSecond(){
         yield return new WaitForSeconds (0.8f);
         GameObject.Find ("AdMobControl").GetComponent<AdMobTest1> ().HandleInterstitialLoaded ();
         Debug.Log("Intestitial Shown");
     }

Thanks!