I have had sex with condom on and he always pulled out before hand. I have never have this happened to me. I am on my period

Update: it wasn’t a tampon cause typically my first day of period is to heavy so I wear a pad. I did go the doctors. It was a part of piece of my cyst, that I am making an appointment to get remove in March. She said she has never seen this happen before and typically explode afterwords. But mine didn’t. She said my bf could’ve put to much pressure on it when having sex. I have nothing to be worried about it as long I take the birth control and doesn’t grow any bigger I should have an easy surgery to get removed.