Boyfriends penis....

Okay... We've been having sex WAY more than usual recently and he said one night it was itchy.. So he rubbed it and it started to bleed. Like it looked like he had grated the head of it on a cheese grater... I don't know how the fuck it happened but we were both shocked. I live with him and I trust him 100%. 
I'm wondering if it's the extra sex we've been having or is it to do with wearing condoms so much??? This morning it looks a lot better but we haven't had sex in 3 days to try and heal it. 
What could it have been? And how can we prevent it from happening again? 
It's not a huge deal I just don't want to see my man in pain. 
Thanks in advance ☺️