I have been suffering from acne for a couple years and have been taking bactrim (sulfamethoxazole and trimethoprim) for 4 months. acne has cleared so can i stop taking the medication?

Yes: You should not take an antibiotic as sole therapy for acne in any case, or any antibiotic for a long time. Your best move would be to stop this and continue whatever topical agent you are using, or topical benzoyl peroxide at least for a while; taper it and see what happens. If you recur, chances are a topical agent will clear you; if not get with your physician.