Birth control?

I told my mom a couple of weeks ago I need to get started on birth control. I told her I need them to regulate my period (which I do), but I also am beginning to be sexually active and would like them just in case. She doesn't know this however, and please do not suggest me telling her because I wouldn't be allowed to see him if I told her that I am sexually active. When I make the appointment, what will they ask me/ do? Thanks for any advice :)