Hey
I would make sure to do a full water change in the tank and make sure to keep it spotless. My next suggestion would be to take out all of the gravel and decorations from the tank so that the organism that causes velvet has nothing to stick to. Try adding a little bit of aquarium salt and putting your fish into a darkened room after doing this. The darker atmosphere will help destress your betta. Make sure to feed him stuff like frozen peas/brine shrimp/blood worms. The healthier the food, the faster he'll get better.
As far as meds go, one of the suggested treatment for velvet seems to be copper sulphate. I really have no idea how you'd get a hold of that or how to treat the fish with it.
All I can say is that I've used the medication you're currently using before and it really does absolutely nothing. It's pretty much a sham.
If you live near a downtown area, there's a huge chance that there will be a little local fish store that can sell you the correct treatment for your fish. If you really are that far away from any pet store, then I'd suggest keeping up with the current medication for the off-chance that it might work until you can figure out something else.
Hoping for the best!