Asking my mom for birth control??? Help!!

I'm 17, I've had a boyfriend for almost a year and a half now. My parents still don't trust us at all. I want to ask my mom if I can go on the pill because my period can be pretty irregular and I'd like to worry less about getting pregnant and doubling up on bc (condom and the pill) seems like a good plan to me. My mom is the type of person to not believe that the pill regulates your period and I'm pretty sure if I ask her she'll think I'm doing it for sex which will probably make it a no. Any ideas?