I am allergic to bactrim and my husband was prescribed bactrim to clear up an infection from a spider bite. While he was on the medication, we had sex and the next morning, I had the rash over my chest like I had previously gotten when I took the Bactrim. Anyway, he has ben finished with the meds for over a month now, and I am still breaking out in the rash after every time we have sex. What could be still causing this. We have been married 11 yrs and I have never had any allergic reaction to him.