What Causes Vaginal Bleeding After Taking Plan-B Followed By Sex?

I m really worried. I had sex a couple of days after my period ended (3 or 4 days after) I took plan b that s same day just in case. Started bleeding 5 days later which seemed like a period to me but it was different. Could it be possible that I got my period 2 times this month? Also, I ve been feeling really bloated. It s really bad.. What are the chances of me being pregant?