I Am 19 And Had Sex For The First Time

I am 19 and had sex for the first time a month ago. I had unprotected sex on a Saturday and took Plan B an hour afterwards. Exactly 7 days later, the following Saturday, I got my period. On Thursday my period stopped and I had sex again on Friday night and Saturday (14 days after taking Plan B) morning. Saturday morning we realized I was still bleeding. I was spotting all day Saturday and on Sunday I was bleeding heavy. It is now Monday and I am still bleeding very heavily. What does this mean??