I bleed the day after sex! HELP!

So I have been friends with benefits with this guy for almost 2 months. And it is absolutely amazing we are really good friends and the sex is mind blowing but, every time after we have sex I get my period the next day. I'm not sure if my hormones are messed up or what's going on I was just hoping for some answers if anyone had this happen to them or what I should do!