I am not suggesting to sue the doctor, as there is no damage done. However, there is medical/doctor monitor mechanism. It is our duty to flag those irresponsible doctors.
I agree that the patient should be more careful. Still, after you mentioned that you are allegic to 青黴素, and doctor still prescribe it to you, the doctor is not a good, responsible doctor. Sure, 青黴素 itself is not a big deal. What if it is something more serious? What if he took the medicine and got bad result? If a complaint can help the doctor to be more careful, it is good for everybody.