How to Ask For Birth Control??

So I’ve been wanting to ask my

Mother to go on BC for a long time, at first it was just for cramps and to regulate my period. Now I’m 15 and I have a boyfriend, I’m not planning on having sex with him anytime soon, but I would still feel a whole lot more comfortable on BC. I’m scared to ask because she’s going to automatically assume my boyfriend and I are having sex. How can I ask her or convince her that sex is not the only reason I want to go on birth control?