20 is too young for sex according to my mom

My mother keeps exiting me and telling me that I am not ready for sex and that I'm too young and that sex will make me undesirable for marriage. She makes me feel that I am a terrible person for having sex and that she will resent me if she finds out that I recently have become sexually active.

She found out that I got birth control and now she won't stop sending me text messages "warning" me about sex.

I'm 20 years old. How to I communicate to my mother that I am old enough for sex?

Edit: I suppose t doesn't help that she hates my boyfriend