RTS game: Camera movement is wierd

I'm building an RTS game and I'm having a problem with the camera movement.

Whatever I move my mouse to the top sreen is not moving really moving the camera view in the front/left/right/back but instead is only changing the values in the axis and the movement is wierd.

So the green arrows is the movement I expect and the red arrows is the movement I get.

I want to say too that, In this game you can rotate the camera in the Y-axis in between 0 and 360 degrees. And in any rotation I want my camera to behave ALWAYS like the GREEN arrows.

  #pragma strict
   
   private var delta : Vector3 = Vector3.zero;
   private var lastPos : Vector3 = Vector3.zero;
   
   public var Boundary : int = 50; // distance from edge scrolling starts
   public var speed : int = 5;
   
   private var theScreenWidth : int;
   private var theScreenHeight : int;
   private var rotationSpeed : float;
   
   var minFov: float = 2f;
   var maxFov: float = 3f;
   var sensitivity: float = 10f;
   
   function Start() 
   {
       theScreenWidth = Screen.width;
       theScreenHeight = Screen.height;
   }
   
   function Update() 
   {
   
        var yCam : float = Camera.main.transform.eulerAngles.y;
   
       if (Input.mousePosition.x > theScreenWidth - Boundary)
       {
          transform.position.x += speed * Time.deltaTime; // move on +X axis
       }
   
       if (Input.mousePosition.x < 0 + Boundary)
       {
          transform.position.x -= speed * Time.deltaTime; // move on -X axis
       }
   
       if (Input.mousePosition.y > theScreenHeight - Boundary)
       {
          transform.position.z += speed * Time.deltaTime; // move on +Z axis
       }
   
       if (Input.mousePosition.y < 0 + Boundary)
       {
          transform.position.z -= speed * Time.deltaTime; // move on -Z axis
       }  
      
      //zoom cam
         var fov: float = Camera.main.orthographicSize;
         fov += -(Input.GetAxis("Mouse ScrollWheel")) * sensitivity;
         fov = Mathf.Clamp(fov, minFov, maxFov);
         Camera.main.orthographicSize = Mathf.Lerp (Camera.main.orthographicSize, fov, Time.deltaTime * sensitivity);
         
         //rotate cam
         if(Input.GetMouseButton(2)){
             if(Input.mousePosition.x > theScreenWidth/2){
                 lastPos = Input.mousePosition;
                 delta = Input.mousePosition - lastPos; 
                 transform.eulerAngles -= new Vector3(0,(theScreenWidth/2-(lastPos.x))*0.01,0);
             }
             
          if(Input.mousePosition.x < theScreenWidth/2){
                 lastPos = Input.mousePosition;
                 delta = Input.mousePosition - lastPos;
                 transform.eulerAngles += new Vector3(0,((lastPos.x)-theScreenWidth/2)*0.01,0);
             }
  
     }
     }