Bleeding during sex.

So the first time I had sex was 1 full day after getting off my period. Afterwards, I went to the bathroom and there was blood, but not too much. I assumed sex had caused my period to come back. The next time after this (about A week and a half later) I bled again. So I searched it. I assumed it was a lack of being wet. So the next time I told my bf what I thought it was so we changed it and made sure I was wet enough. I still bled. We have both only had sex with each other. What could it be ? Also, it has hurt at the beginning every single time.