Sorry to hear. I know the feeling. I'm in a similar situation with mine. Except he's a bit more active, using the bathroom regularly, but seems to be going downhill regardless of the meds and upping his food. So I'm there with you!
Hope yours gets better. It does take a long time. I had a chameleon with severe MBD, who survived by some miracle. But after almost 8+ months of recovery and rehab he's doing a lot better now. All I can say is PATIENCE. it's going to take a lot of work, care, but mostly patience. I wanted to give up sometimes, but it's worth it in the end.