I've taken bactrim (sulfamethoxazole and trimethoprim) ds before, why now would i get a rash? also what should i do to get rid of it?

Having reaction: Would see your doctor. Likely you are having a reaction to the medication. Would stop it right away.

Get evaluated. : It is possible to develop drug sensitivities after multiple prior exposures. First you must stop the offending agent, make sure it is the Bactrim and not another medication or food. If it is the bactrim, you need to switch to another antibiotic to complete therapy, depending on the reason for the antibiotic. Get evaluated, especially if the rash worsens. Benadryl (diphenhydramine) may help, creams are unlikely to.

See your DR.: The more often you are exposed to a med the greater the chance of becoming allergic to it. Bactrim (sulfamethoxazole and trimethoprim) is a very common cause of allergic rashes. Sometimes they are serious. Now you must avoid this med forever. Antihistamines will not help unless you have hives. The rash may bother you for several weeks. Your dr. May wish to help you with a few doses of a steroid such as Prednisone 20mg alternate days.