No dont go to your doctor, all the doctor does is treat the symptom not the problem. Doctors just prescribe medication that looks like it should go with the symptom. Any herbalist or naturist can help you. Once you get their advice then order your own powders and herbs online and capsulate it yourself, much cheeper. One option is either his body fluids or your body fluids are to acidic for the other person or himself. I had the same problem but I would get it after anytype of sexual activity even masterbation. I started drinking ionized alkaline water and i no longer have that problem. See and no doctor visit, crazy meds or side effects to put up with.
you should talk to the doctor about this. its odd hes getting a rash even after oral sex.
when he prescribed him medication he should and likely told him whats going on