I went to the er monday night and was told i had a bad case of cellulitis. how many days should the bactrim (sulfamethoxazole and trimethoprim) take to stop the stinging?

Treat until better: Sometimes the pain and inflammation of cellulitis takes a few days to go down. That's because of the injury the bacteria have caused. Good that you've been seen by a doctor -but you need follow up care to make sure you are responding well. If you have co-morbid illnesses like diabetes, then you definitely need more care, not less. Try to elevate the area (or stay off it) to help ease the pain.