How do I start the pill?

I'm sexually active with my boyfriend and we use condoms every time but I want to start a form of birth control for more peace of mind as well as period relief. My mom thinks i'm still a virgin and that i'm not sexually active at all with my boyfriend. I don't know how to bring it up without her thinking I want to go on the pill because I don't want to get pregnant. Should I come clean and tell my mom what my boyfriend and I are up to when we are alone or should I mention the pill to help with my period? Please share some of your advice.