Hey girl:
the bump on your vagina could be a cist, especially since you have it for the past 2 years and you never had sex. Don't be ashamed to tell your mother, after all she is your mother and a woman. You should consult a gynecologist as soon as possible. Your mother should go with you.
Or, see your school nurse.
Don't worry until you know for sure what it is.
Good luck girl.