How do I tell my mom I want birth control

I’m 17 years old and I’ve been dating the same guy for about a year and a half, we started having sex a couple months ago. My issue is that I want to be put on birth control just to ease my worry of ever getting pregnant but also because I always have really bad periods every month. The thing is I have no idea how to tell my mother about this, she knows I’ve been having sex and I’ve told her multiple times about my terrible periods. I’ve tried having this conversation with her many times but she never listens. Someone plz give me some advice.