WaitForSeconds in c# not working

Hi, my code stops when the 3 shows up. I think there's something wrong with the yield line. Please help.

 using UnityEngine;
 using System.Collections;
 
 public class PauseScript : MonoBehaviour {
     public GameObject pauseBackground;
     public GameObject pauseButton;
     public GameObject playButton;
     public GameObject coinText;
     public GameObject scoreText;
     public GameObject unpauseCountdown;
     public static int number=3;
     public void Pause(){
         pauseBackground.SetActive(true);
         playButton.SetActive(true);
         pauseButton.SetActive(false);
         coinText.SetActive(false);
         scoreText.SetActive(false);
         for(int i=0;i<ClickController.cubes.Length;i++){
             ClickController.cubes[i].SetActive(false);
         }
         Time.timeScale=0;
         ClickController.onPause=true;
     }
     public void Unpause(){
         pauseBackground.SetActive(false);
         playButton.SetActive(false);
         pauseButton.SetActive(true);
         coinText.SetActive(true);
         scoreText.SetActive(true);
         for(int i=0;i<ClickController.cubes.Length;i++){
             ClickController.cubes[i].SetActive(true);
         }
         StartCoroutine ("countdown");
     }
     public IEnumerator countdown(){
         Debug.Log (2);
         unpauseCountdown.SetActive(true);
         unpauseCountdown.GetComponent<TextMesh>().text=number.ToString();
         number--;
         yield return new WaitForSeconds(1);
         StartCoroutine ("countdown1");
     }
     public IEnumerator countdown1(){
         Debug.Log (2);
         unpauseCountdown.SetActive(true);
         unpauseCountdown.GetComponent<TextMesh>().text=number.ToString();
         number--;
         yield return new WaitForSeconds(1);
         StartCoroutine ("countdown2");
     }
     public IEnumerator countdown2(){
         Debug.Log (2);
         unpauseCountdown.SetActive(true);
         unpauseCountdown.GetComponent<TextMesh>().text=number.ToString();
         number--;
         yield return new WaitForSeconds (1);
         StartCoroutine ("countdown3");
     }
     public IEnumerator countdown3(){
         yield return new WaitForSeconds (1);
         Debug.Log (3);
         Time.timeScale = 1;
         unpauseCountdown.SetActive(false);
         ClickController.onPause = false;
         number = 3;
     }
 }