Welcome to PT.

I commend you for your dedication to Sox. You will see the light at the end of the tunnel.
I've nursed a lot of sick cats. One of my cats lived in a cat bag with only his head sticking out for 6 weeks. He paws were infected and he self-mutilated.

I'm sure Sox appreciates your efforts.
You are doing good by him.

I would continue the A/D and add Nutrical to it. Available at pet stores.
make it into a slurry and pull it up into a needleless syringe.

It only takes about 30 cc's a day to keep a cat going until the meds do their thing.

There is also something called Feline Rebound Diet. It can be used longterm.
It is an RX through your vet.

I hope you get to the source of his problems, so things can get back to normal.

We are here for you.