Afraid to tell my mom

My mom thinks that I'm still a virgin and I've been kind of stuck with guilt lately because of it. She always mentions things about how's she's proud that I've saved it and how stupid it is when teenagers have sex and how glad she is that I'm not like that. I'm 17 and I've had a boyfriend for 2 years but we've only been having sex for a couple months. I am also on birth control because of medical reasons but she still doesn't suspect it. I can't really tell sometimes if she actually suspects the truth just because I've been in a long term relationship and it's bound to happen sometime or she just has that much trust in me and I know she's not stupid or anything she's very smart and I have a lot of respect for her. I'm not sure if I should just tell her the truth or not because I don't know how she will react and I don't want her to look at me differently or even my boyfriend differently. I have no idea what to do because I don't want to deal with her bringing it up all the time because I know she will. Please help! Comments please :)