Battling coccidiosis, need help

I have a flock who is affected by coccidiosis. Hens had pasty discharge and red butts with feather loss the entire year and a half I had them. I thought this was vent gleet and tried many remedies for that including yogurt, apple cider vinegar, probiotics, and diotemaceous earth. Recently had to move chickens to smaller quarters, and then one had severe discharge. I took to an avian vet who cultured the discharge and looked at it under a microscope. She diagnosed coccidiosis and prescribed SMZ TMP, Metacam oral, and silver sulfadine ointment for her bottom. Initially noted improvement but then discharge came back. Also treated rest of flock with Corid 1/2 tsp. to 1 gallon of water x 5 days. Initially saw improvement in some of the birds who were depressed, then today on the fifth day noted my favorite rooster acting kind of quiet. Should I administer the Corid for another course or switch over to Sulmet or what should I do? Please help. They are hanging in there and I want to help them.