Feeding schedule?

My baby is 9 weeks and every time I take her to the doctor she asks about her feeding schedule and how often she eats and how much.  But I don't have her on a schedule. I just watch her and let her tell me when she needs to eat and any time she acts hungry I feed her. I haven't noticed a pattern but she never goes hungry. I nurse her whenever I can and then give her formula if she's still hungry after that and I keep feeding her until she stops. Am I doing this wrong?