A bump? Like a pimple?
Thing is, at 13, stuff is changing. (Breasts that used to be soft and flat are now sore and feel harder, etc.) It's possible what you're feeling is normal. It could also be an ingrown hair. Do you have a good family doctor that you trust? Do you think your mom would take you to an ob-gyn (doctor specializing in obstetrics and gynecology, the kind who does pap smears and other things) if you asked? (They see vaginal areas all day, every day, so wouldn't be bothered in the slightest to look to see the bump, and they could tell you in a heartbeat if it was normal or not.) If your mom is open to helping you get an ob-gyn, see if you can get a woman doctor, it is so much easier when you first get this kind of doctor for her to be female.
If that is all out of the question, try taking some sitzbaths (shallow baths where you soak for a while). If it is an ingrown hair, it should open and drain if you do one a night.