A week ago, I got on one of those stationary exercise bikes. I was on it for about 10 minutes. When I got off, I noticed that I was bleeding, and it hasn't stopped. It's going on 8 days now. I'm on birth control, so my periods are regular, now. I haven't had sex in almost a month. I had my period last month and I have another week until I'm supposed to start again. Any ideas as to what could have caused it? Could it just have been because I haven't ridden a bike in awhile and the way I was sitting on it, or is it something more serious?