what do I do?!

I want to be on birth control, not only because I am sexually active but because it will help my period. Frankly, my mother is psychotic. and if I say one thing about being on birth control she will assume it's for sex. my boyfriend is 18 and I'm 16, he could get arrested for having intercourse with me. and there's no telling if my mom would call the cops. idk what to do??? would the doctor keep it confidential???