Dick bleeding

Ok so last time I had sex my boyfriends dick started bleeding. It wasn't a lot but it's the second time in a span of 5 months that it's done this. The first time we thought it was just him going to hard hitting it from the back but this time, also in the same position, it happened again. It doesn't happen every time he goes from the back but idk what it is and he's soooo stubborn and won't go to the doctor unless it happens multiple times. What could it be do you guys know?