Blood after sex??? HELP

I keep bleeding after and during sex, at first I thought it was my period but then I checked and realized I've been off it for 3 days with absolutely no extra bleeding whatsoever until I decided to have sex today, I had it three times wi h my boyfriend (we haven't seen each other in a week) and the first time there was just a little bit of blood and I didn't even notice, the second there was a bit more and I ended up seeing it on my leg, now I'm sitting recovering from the third time because there is a lot more blood and I have some cramps going on. Has anyone else experienced this and should I be concerned???