I used to have sharp pains in that area when i was a kid and into my teen years. I never did find out what it was, but it passed.
Your mom really needs to take you to a doctor. If you were my child, i'd take you. There's no sense walking around feeling fearful about a symptom you have.
do you have a school nurse? If so, see if you can discuss it with her, or if you know someone who is a nurse, perhaps they could help. One or the other of these people may help you talk with your Mom, too (if you ask them)