Suggest Remedy For Rash And Burning In Vagina

i am a 20 year old female. I have been having frequent protected sex with my partner for a while now, and now that i'm on the pill, we decided to try unprotected. I get a rash and burning right afterwards (NOT a yeast infection or a UTI, because i got tested and came out negative for both.) I believe i might have a sperm allergy. i can tolerate it, but my worry is that it will get worse over time. is this a legitimate worry? if so, what can i do about it?