Mouse-controlled camera getting stuck.

I'm a total noob to unity, and I was trying to get a rudimentary mouse-controlled camera. I have some basic code, and looking horizontally and vertically is fine. However, when I'm looking around the z-rotation of the camera changes, rotating the view weirdly, and when I turn around so the rotation around the y-axis is 180, I can't look horizontally or vertically, it gets locked and if I try to look away it only affects the z-axis rotation, which shouldn't be changed in the first place. Here's my script in the main camera:

 var xdirection : float = 0.0;
 var ydirection : float = 0.0;
 var cenw : float = Screen.Width/2;
 var cenh : float = Screen.Height/2;
 function Update () {
     var mousex : float = Input.GetAxis("Mouse X");
     var mousey : float = Input.GetAxis("Mouse Y");
     
     if (mousex != Screen.width/2 && mousey != Screen.height/2) {
         xdirection += (mousex*0.4)- cenw*Time.deltaTime;
         ydirection -= (mousey*0.4)-cenh*Time.deltaTime;
     }
     else {
         xdirection = 0;
         ydirection = 0;
     }
     
     xdirection = Mathf.Clamp(xdirection,-90,90);
     ydirection = Mathf.Clamp(ydirection,-90,90);
     
     transform.rotation.x = ydirection;
     transform.rotation.y = xdirection;
     
     Screen.lockCursor = true;
 }

The main camera has a rigidbody and a capsule collider. I've tested it without both components and I get the same issues. "cenw" and "cenh" are the x and y coords for the center of the screen.