What Causes Burning Sensation On The Penis During The Intercourse?

Hi I have a situation that I have been trying to sort out for about a year and a half now. I have ruled out some options and it has left me asking a strange question. I have been dating my boyfriend for about two and a half years now, I have the paragard IUD, and we do not use condoms. We ve been sexually active for two years now and very happy except that over the past year or so every time we have sex, his penis gets a burning sensation, it is red and the skin starts to peel off. If he washes it right after we finish, it usually isn t that bad. We ve been in a long distant relationship over the past year so it is very easy to detect where this is coming from. We ve ruled out any STD s, yeast infections, the possibility of it being any soaps or anything I use. So we are wondering if it is possible for him to be allergic to me. To go along with this, whenever we have oral sex, his throat gets itchy and irritated as if he s having a mild allergic reaction. I hope there is someone that can help us because it s starting to effect our relationship.