I can't talk to my mom about sex

I'm 17 years old and my mom always tells me that I can talk to her about everything. The only problem with that is, any time I DO talk to her about anything she either flips or doesn't want to talk to me about it.
I lost my virginity a few weeks ago and I haven't told her (obviously. I'd never be allowed to spend time with my boyfriend outside of my house ever again!) and I feel weird even talking to her about sex related topics because I have to play dumb and by now I know that I can't tell her at all. Ever. Well, maybe when I move out I can.
Does anyone else have a similar problem? And if you have in the past, is there anything I can do to break down this barrier between me and my mom?