Hi, This Is A Very Personal Question, So Bare With

Hi, this is a very personal question, so bare with me. I'm 16, and a female. Me and my girlfriend have been having sex for awhile now. In the beginning, everything was fine. But a couple of months ago, she "popped my cherry". And ever since then, every time we have sex, i always bleed. Do you know what could be the cause of this?