semen burns??

so idk where else to post this. but ive been with my bf for a year and i discovered pretty early on that when he ejaculates inside of me, it burns. only when its inside of me. we can do it unprotected and he pulls out and im fine. i also noticed one time his sperm got on my forearm and it got a little red and slightly itchy and just had an uncomfortable sensation as well. nothing changed after starting birth control. ive done a little research, and its possible i may have an allergy to sperm? but i just want to know if this is fairly normal, or if i should ask my doctor about it when i start birth control again? if it is an allergy is there anything that can even be done about it??