i was prescribed Bactrim 500mg 2x daily about a week ago for a abscess in my belly button. i took it for about a week and it helped alot. but yesterday morning i noticed a red rash on my right forearm. and throughout the day it progressed up my arm more and more. now today it is all over both arms and hands. on the top of my chest very minor. and on both feet and legs. and it is still getting worse. i'm assuming its an allergic reaction but its been almost a week of taking it and it just now showed up? the rash is not bumpy. just a little itchy sometimes and warm to the touch. is there any need for concern or medical treatment? i have stopped taking the pill.