Why does it flip me around and around (First Person)

I had this working a few weeks ago and I have and used the same code in another project and it flips me around and around.
The ‘Player’ is a empty game object and has a capsule collider, rigid body attached to it and the character controller attached to it plus this code.
(the ‘player’ also within its folder thingy/under the ‘player’ is the camera and 3d object capsule connected to it)
Any help would be most appreciated!
Code:

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

public class PlayerController : MonoBehaviour
{

[SerializeField] Transform playerCamera = null;
[SerializeField] private float mouseSensitivity = 3.5f;

[SerializeField] private float movementSpeed;

[SerializeField] private float walkSpeed;
[SerializeField] private float runSpeed;
[SerializeField] private float runBuildUpSpeed;
[SerializeField] KeyCode runKey;

[SerializeField] float gravity = -25.0f;

[SerializeField] [Range(0.0f, 0.5f)] float moveSmoothTime = 0.3f;
[SerializeField] [Range(0.0f, 0.5f)] float mouseSmoothTime = 0.03f;

[SerializeField] bool lockCursor = true;

private float cameraPitch = 0.0f;
private float velocityY = 0.0f;
CharacterController controller = null;

Vector2 currentDir = Vector2.zero;
Vector2 currentDirVelocity = Vector2.zero;

Vector2 currentMouseDelta = Vector2.zero;
Vector2 currentDeltaVelocity = Vector2.zero;

private void Start()
{
    controller = GetComponent<CharacterController>();
    if (lockCursor)
    {
        Cursor.lockState = CursorLockMode.Locked;
        Cursor.visible = false;
    }
}

private void Update()
{
    UpdateMouseLook();
    UpdateMovement();
}

private void UpdateMouseLook()
{
    Vector2 targetMouseDelta = new Vector2(Input.GetAxis("Mouse X"), Input.GetAxis("Mouse Y"));

    currentMouseDelta = Vector2.SmoothDamp(currentMouseDelta, targetMouseDelta, ref currentDeltaVelocity, mouseSmoothTime);

    cameraPitch -= currentMouseDelta.y * mouseSensitivity;
    cameraPitch = Mathf.Clamp(cameraPitch, -90.0f, 90.0f);

    playerCamera.localEulerAngles = Vector3.right * cameraPitch;
    transform.Rotate(Vector3.up * currentMouseDelta.x * mouseSensitivity);
}

private void UpdateMovement()
{
    Vector2 targetDir = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
    targetDir.Normalize();

    currentDir = Vector2.SmoothDamp(currentDir, targetDir, ref currentDirVelocity, moveSmoothTime);

    if (controller.isGrounded)
        velocityY = 0.0f;

    velocityY += gravity * Time.deltaTime;

    Vector3 velocity = (transform.forward * currentDir.y + transform.right * currentDir.x) * movementSpeed + Vector3.up * velocityY;

    controller.Move(velocity * Time.deltaTime);

    SetMovementSpeed();
}

private void SetMovementSpeed()
{
    if (Input.GetKey(runKey))
        movementSpeed = Mathf.Lerp(movementSpeed, runSpeed, Time.deltaTime * runBuildUpSpeed);
    else
        movementSpeed = Mathf.Lerp(movementSpeed, walkSpeed, Time.deltaTime * runBuildUpSpeed);
}

}

Try Constraint rotation in rigidbody in which axis you want to clamp