Are you usually on top? I find I get achy-er when I am after not for a while. Not that it stops me. I figure I just stretched some new muscles and should do yoga.
I really don't know on the cheese grater thing. I read someone else mention it in another thread, but their solution was foreskin restoration and not remotely practical. Have you been tested for BV and yeast? Those can cause quite a bit of irritation, but if you have a mild infection you might only notice it after sex. I've had friends who had very long term issues with each of those. I think their husbands ultimately had to be treated as well. Randomly, when I eat dairy I get irritation in my digestive tract, like all the way down. At its worst, that irritation causes quite a bit of discomfort with and after sex, too.