blood!?

Last night I had intercourse with my fiancé. I had stopped taking BC about two or three days ago during the time I took BC I had a much longer menstrual which my doctor  told me was normal. Well after about a week I wasn't bleeding so much but more so spotting and it was a brown color and not very heavy. I had intercourse around this time, no pain, no blood, nothing. (Which is strange because usually when I have sex after a period there is blood even if it's not much) well last night I had some excessive bleeding and it kind of threw me off because I hadn't bled the other night so why all of a sudden? There was no vaginal pain, some abdominal but that's all. Any theories?