What to do if you receive rash and fever while taking sulfa?

Stop, stop, stop !!!: Sulfa allergies can develop into extremely severe reactions. That is likely to be what is happening to you (allergic reaction). You should immediately discontinue the sulfa drug and return to your doctor to have them substitute an alternative medication for what the sulfa was treating, and for them to assess the severity of your allergic illness.

Stop, see doctor: There are two possibilities here: either you are having a reaction to the sulfa drug, or the infection that you're treating with the drug (which i'm assuming is an antibiotic, though not all sulfa drugs are) is getting worse. Either way, you need to stop the drug and check with the doc who prescribed it.