needing help

I recently have become sexually active. I asked my mom months ago if I could get on birth control(before I was having sex) and she said no, that is a hassle and all this stuff. I want to ask her again but I don't want to tell her I'm having sex, I want to get on birth control for many reasons but don't know what to do if she says no. I can go to the health department and get on birth control but it may make my period irregular. I need advice!!!