Unity camera spinning around uncontrollably

I'm trying to clamp the camera rotation but when doing so the camera spins out uncontrollably. I tried it with Math.fClamp and another way and both seem to do the exact same thing.

Here is the code that I use: using UnityEngine; using System.Collections;

 public class CameraController : MonoBehaviour {
 
     
     float mRotY;
     
     void Start () {
         if(rigidbody)
             rigidbody.freezeRotation = true;
             
         if(!Debug.isDebugBuild)
             Screen.lockCursor = true;
         else
             Screen.lockCursor = false;
         
     }
     
     
     void FixedUpdate () {
         
         mRotY = Input.GetAxis ("Mouse Y") * GameManager.sensitivity * Time.deltaTime;
         if(mRotY>270.0f)
             mRotY = 270.0f;
         if(mRotY<90.0f)
             mRotY = 90.0f;
 //        
         transform.Rotate(mRotY, 0.0f,0.0f);
         
     }
 }