birth control

So I didn't really know where I should put this. But I'm just going to put it here. So me and my boyfriend have been having sex pretty often now. We've been together for awhile. And I've been wanting to get on the pill just for emergency and it would help with my period. But for me to do that, I would have to talk to my mom. And I just don't really know what I would say to her. Any suggestions on what I should say to her about this?