What do you think it is?

I had sex on the 5th and 9th of may, took my period as normal on the 11/12th , lasted a week as normal but for a few days after it I felt sick and had really bad cramps. So three days ago I woke up with my period again, and it had came right through my pjs really badly and same yesterday when I woke up. But now today, the third day, it seems like they are ending. My belly has also got really flat and boobs bigger, not sure if its just a coincidence?