Have been diagnosed with suspected parasitic infection. When I take 100mg bactrim (sulfamethoxazole and trimethoprim) a day it's under control, flares up otherwise. Request advice on med?

Parasite infection. Bactrim (sulfamethoxazole and trimethoprim) is an antibiotic which means its chief effect is on bacteria, not parasites. That said, Bactrim (sulfamethoxazole and trimethoprim) does work for cyclospora and isospora- parasites that cause diarrhea. It doesn't make sense that your symptoms return after a treatment course- unless you are getting re-exposed somehow in your environment or something "unrelated" to these purported parasites is occurring. Best to go see an MD.
Parasitic infection. Cannot imagine what parasitic infection is likely to respond to therapy with Bactrim (sulfamethoxazole and trimethoprim). You really need to be seen and discuss this with a doctor who can have access to your records and examine you. Preferably an infectious diseases expert. Good luck.