I wanna get on birth control

So I'm 15 And I've been having sex but my mom doesn't know. She thinks I'm a virgin n stuff. But anyway I wanna get on birth control but idk how to convince her to get me on it. Like I can't tell her I'm having sex bc she'll kill me but I also wanna be safe or whatever when it comes to pregnancy since I recently thought I was and was freaking out. Or can I get it somehow without her consent?? I live in Oklahoma and laws are dif everywhere and ive dome some research but i think it depends and stuff. What should I do ???