Can anyone tell me if they had an experience where they just drop...

Can anyone tell me if they had an experience where they just dropped interest in their b/f at all? This is a guy concern, of what it does to girls, and its not the best thing. I know a lot of girls, and I have talked to a lot. Yasmin has seemed to do the worse so far as I noticed. my g/f is taking Yasmin. Our relationship was really tight and close. everything was going perfect. the night we had a dance, everything was perfect. we were being ourself. the next day she just snapped, and she was not herself. she is opposite of herself right now, and we are on the worse conditions. I don't want it to end, and it seems as it is. she just lost interest of everything we had, just hanging out and everything. her friends told me she is changing also, and no one knows. I have been reading a lot lately on this, and it seems that it is this birth control, Yasmin some people had the same exact problem. I suggested to her that it could be the birth control is why she is acting like this, but she disagrees. we have not talked in 3 days now, and everything is not right. I do not like this birth control, and if she does not want to get off birth control, I would like her to switch perhaps. She is not herself anymore, and I am not sure how to show her this. I just don't understand how it could all affect a person to be their opposite self. any ideas of what I should do? I wanna fight this through everything and be there for her. a lot of people say she is not herself anymore, and I want to help with everything I can do. both of our ages are 17, young yes, but I want to understand a few things and I want to keep this relationship alive.