Getting birth control


I’m still a Virgin but I’ve been thinking over the thought of having sex and I’m ready. I hear stories of girls using condoms and still getting pregnant, I want birth control as a back up and to possibly help regulate my super irregular period. But my mom is extremely against it and is irrational, I can’t tell her I want to have sex because she is very old fashioned. How do I convince her to let me have birth control ??