Bleeding after sex.

So me and my bf just got done having sex...well he stopped because he saw a little blood on his penis and freaked out. I'm not that worried I just want to know if bleeding can happen after deep penetration? My period doesn't start till May 6, so I know it's not period I'm just curious if this happens to alot of women. This is a first for me, but like I said im not worried about it.