Do you mean rough sex- a lot of friction, maybe dry? Where are they?
They could be irritated oil glands.
Next time you have hard sex, use some extra lube - use water based or silicone lube if you use condoms - and see if that helps.
https://www.gq.com/story/the-best-sex-lube-for-every-level-of-freakiness
https://www.bustle.com/p/the-6-best-lubricants-for-condoms-12218725
Check with your partner first to make sure they don't have any allergies.
If it happens after, have a doctor take a look.