I found out I'm also allergic to sulfa drugs when I got a very bad sinus infection and my Doctor figured it was a good inexpensive solution. She said itching was part of the reaction and I felt itchy right after starting it but figured I was being paranoid. I took it almost the whole course then started having night sweats and fevers and the shakes. I thought I was also getting the flu and went to work and everyone asked me what was wrong with my face. I was home alone as sister had gotten hurt at work and was staying with mom to heal a bit so hadn't really looked in the mirror or had any one else looking at me. I had like a measles/sunburn rash all over me and it was even in my ears. Doc put me on something else way cheaper real quick and the rash and the sinus infection cleared in a few days. I peeled just like a sunburn too. I'm also allergic to penicillin and had a similar reaction as a baby, maybe they're related.