Lerp going crazy when negative

Lerp starts rotating hundreds of times on every axis only when changing from a positive Y value to a negative Y value. I've been stuck on this for more than two hours and quaternion.lerp hasn't been working so I'm using Vector3.Lerp. I really need help here!

 this.gameObject.transform.localEulerAngles = Vector3.Slerp(this.transform.eulerAngles, new Vector3(0, desiredRot , 0), rotTimer);

Thanks in advance !