Please don't stop cleaning his tank. I really stress that you should get a master test kit to test the water for ammonia, nitrites, and nitrates. These are all toxins found in tanks, and build up when the tank is uncycled. Also, be careful when you mix medications, this can have harmful effects. The best cure for anything a fish has is clean water and a little plain (non-iodized, non-anticaking) salt or salt specialized for freshwater aquariums. When you use antibiotics and antifungal medication you need to change the water more often. The medications kill the beneficial bacteria as well as the harmful bacteria in the tank.
BC_mom: in natural water, there are cycling agents that reduce ammonia and nitrogens. The water is changed through natural processes such as the billions of bacteria that turn the ammonia into nitrites, other species of bacteria that use the nitrites and produce nitrates, and plants that take in the nitrates. In a tank setting, the humans have to foster the growth of this bacteria, and these medications kill it off. Keep in mind also that in the wild, bettas have thousands of gallons of naturally cycled water on a regular basis.