Starting BC

So I'm 17 and want to get on birth control to help with my super heavy periods but I don't know how to talk to my parents about it. I also have a boyfriend of a year and a half so I'm afraid my parents will think it's because I'm having sex even when I tell them I'm not. (We're not ready for it-we don't plan on it even after I start BC) How do I bring it up with my parents and make them believe it's only for my periods? Thank you ❤️