Asking for birth control

I'm afraid to ask my mom to be put on birth control. Ever since I hit puberty (9), she continuously tells me that sex is for after marriage. She was already very strict about dating, so she's bound to be even more so about sex. (However, this is not something I wish to live by). I'm 17 and I just want a little extra protection - decreasing my chances of pregnancy even more. But I'm way too scared to ask.  Are their any ways that I can possibly get birth control on my own? Or does any one have any advice as to how to get the OK from her?