This Doesn't Happen After Every Time My And My Girlfriend

This doesn't happen after every time my and my girlfriend have sex, but lately it feels like it's been more frequent. After sex, sometimes my foreskin and some skin around the middle of my penis has gotten red and my foreskin has gotten slightly swollen. This usually goes away after a couple days, but I have no idea why its happening. I practice great hygiene and so does my girlfriend. After sex, the skin feels a bit sensitive, almost like a sunburn does. It doesn't itch at all but I feel like this isn't normal. What could be causing this and how can I stop it?