Rash after sex

So, my bf and I just did it. He’s got a rash on his lower stomach close to his right pecs. He’s flipping out scared shitless now. We used protection and changed condoms a lot to avoid STD and STI we have no past history of other sexual encounters. I told him it’s over stimulation so I gave him an allergy pill. It seems to go away by now. What should we do? There’s a medical clinic nearby.