Birth Control Help

so i want to go on birth control because my periods get really bad. i'm so heavy that it's like a crime scene. i bleed through all of my clothes even when i'm wearing a pad. i even bled through sheets at night. my periods are also irregular and i want to even them out. i'm 17 and i do have a boyfriend which is why i think my mom won't let me go on it. i worried she's gonna think that i'm just doing it because of sex even tho i personally don't feel ready to have sex right now or in the near future. how should i go about telling her and asking her if i can go on birth control? Any suggestions would be so helpful!!