Mother against the pill

Im a teenager in high school, and ive been with my boyfriend for a year now. We're very much in love and just started having sex. We used a condom the first couple times and it worked just fine, but i'd feel so much better on the pill as well. However, my mother (a strong christian) is against it. She doesn't know of my sexual activity and id like to keep it that way. Ive tried to get on it because of my period, but she still refuses. I want to be safe, but I also want to continue my sexual activity. How do I talk to her about this and get on the pill?!