Sorry hear about this!!

Is your vet a good herp vet? How come no blood was taken?

I hope he gets well. Just keep up on those doctor visits and their instructions. Maybe even get a second opinion. I know what it's like to have a sick herp! My collared was sick for months and I spent hundreds if not thousands with multiple vets including driving out to Cornell University with specialists there. It will be worth it in the end when your turtle is happy and healthy again. I'll pray for him!