Teen birth control help please!

So I am nearing 15 and my boyfriend and I are wanting to be sexually active. We've discussed it and decided that were aren't  risk having sex until I can go on BC because though we plan on using condoms too, they can break. I want to go on birth control but I'm not quite sure my mom is up for that. For AGES I've complained that my cramps are horrible and my period is irregular and finally my dad was the one who asked if I had talked to my doctor about starting birth control! However throughout my attempts trying to get my mother to mention birth control as an option because of my cramps she has instead offered me the painkiller things her doctor perscribed her when she gave birth to my infant brother. I really don't know what to do. I highly doubt  my mom would be comfortable knowing I want to be sexually active or even me starting birth control because she's not naive enough to let me get it for so said cramps. What do I do? Could I access birth control without my mom knowing?