onmousedown issues

for some reason on the object print will run on the 0 click but never on the 1 or 2, why also the code never runs for anything other then 0??????

using System.Collections; using System.Collections.Generic; using UnityEngine; using UnityEngine.UI;

public class PlanetName : MonoBehaviour {

 public Text PlanetInfo;
 public bool TextShowing;
 public string planetName;


 // Update is called once per frame
 void Update () {



 }

 void OnMouseDown(){





         if (Input.GetMouseButtonDown (0)) {

         print("hit");

             //    Debug.Log ("true");
             PlanetInfo.gameObject.SetActive (true);

             PlanetInfo.text = planetName;

         }

         if (Input.GetMouseButtonDown (1)) {
                        print("hit");



             //    Debug.Log ("true");
         PlanetInfo.gameObject.SetActive (false);

             PlanetInfo.text = planetName;

         }



     }



 }