Yaw and Rotation camera issue

I slap this script to the camera which is a child object in an invisible sphere.
It works really nicely as a free roaming camera script but there is one issue: using Q and E for rotation doesn't add up with the 'free look while holding middle mouse button' so it flips to a straight rotation when you click fire3
I seem to be lacking the skill to figure this out... Everything that involves rotating things seems to paralyze my mind. Anybody who can help out?

Code (CSharp):

1.  
2. using UnityEngine;
3. using System.Collections;
4.  
5. public class Camera : MonoBehaviour
6. {
7.     public float RotationSpeed = 60.0f;
8.     public float KeySpeed = 7.0f;
9.     public float ScrollSpeed = 50.0f;
10.     public float MouseSensitivity = 4.0f;  
11.     private float yaw = 0.0f;
12.     private float pitch = 0.0f;
13.     float minHeight = 200f;
14.  
15.     void Update()
16.     {
17.         Vector3 currentPosition = transform.parent.position;
18.         float height = transform.parent.position.y;
19.  
20.         // WASD keyboard input
21.         if (Input.GetKey(KeyCode.W))
22.             transform.parent.Translate(Vector3.forward * Time.deltaTime * KeySpeed);
23.         if (Input.GetKey(KeyCode.S))
24.             transform.parent.Translate(Vector3.back * Time.deltaTime * KeySpeed);
25.         if (Input.GetKey(KeyCode.A))
26.             transform.parent.Translate(Vector3.left * Time.deltaTime * KeySpeed);
27.         if (Input.GetKey(KeyCode.D))
28.             transform.parent.Translate(Vector3.right * Time.deltaTime * KeySpeed);
29.  
30.         // QE rotation
31.         if (Input.GetKey(KeyCode.Q))
32.             transform.parent.RotateAround(currentPosition, Vector3.up, (-RotationSpeed * Time.deltaTime));
33.         if (Input.GetKey(KeyCode.E))
34.             transform.parent.RotateAround(currentPosition, Vector3.up, (RotationSpeed * Time.deltaTime));
35.  
36.         // scrollwheel to lower or raise camera
37.         if (Input.GetAxis("Mouse ScrollWheel") < 0)
38.             transform.parent.Translate(Vector3.up * Time.deltaTime * ScrollSpeed);
39.         if (Input.GetAxis("Mouse ScrollWheel") > 0)
40.             transform.parent.Translate(Vector3.down * Time.deltaTime * ScrollSpeed);
41.  
42.         // Free look while holding middle button
43.         if (Input.GetButton("Fire3"))
44.         {
45.             yaw += MouseSensitivity * Input.GetAxis("Mouse X");
46.             pitch -= MouseSensitivity * Input.GetAxis("Mouse Y");
47.             transform.parent.eulerAngles = new Vector3(pitch, yaw, 0.0f);          
48.         }
49.  
50.         if(height < minHeight)
51.         {
52.             transform.parent.position = new Vector3 (transform.parent.position.x, minHeight, transform.parent.position.z);
53.         }
54.  
55.     }
56. }
57.  

 

solved it, update transform.parent.eulerAngles.y when Fire3 is clicked:

Code (CSharp):

1.         // Free look while holding middle button
2.         if (Input.GetButtonDown("Fire3"))
3.             yaw = transform.parent.eulerAngles.y;
4.         if (Input.GetButton("Fire3"))
5.         {          
6.             yaw += MouseSensitivity * Input.GetAxis("Mouse X");
7.             pitch -= MouseSensitivity * Input.GetAxis("Mouse Y");
8.             transform.parent.eulerAngles = new Vector3(pitch, yaw, 0.0f);
9.             print(yaw);
10.         }

Thanks self!