He needs to be dewormed regardless of what the vet or vet tech saw on the fecal, as some things like Giardia, coccidia and tapeworms aren't usually caught on a fecal float. Flagyl or Albon works well for protozoan/flagellates and some pyrantel pamoate(Strongid) or fenbendazole(Panacur) works well to get rid of pretty much anything else. I would also get the vet to give him some subcutaneous fluids, with some lactated ringer's solution(for electrolytes) or just place warmed saline.

What type of enclosure is he set up in? I have a small male that weighs about 50g, was dehydrated when I got him, had mites(gone now thanks to Provent-A-Mite) and was just overall a skinny little dude. He's in a 12qt tub with his heat 94 on warm side and 84 on cool side, a small water bowl, two plastic saucers, newspaper for bedding and is due to eat tomorrow. We'll see. He's been settling in for about 2 weeks now, handled once for tub cleaning.

I would try to increase his heat a bit and get him deparasitized. That is probably his main concern right now. Maybe try to get some acidophilus into him too as his gut flora may not be working as it should. Handle him as infrequently as possible and keep him in a dark, quiet place. Maybe do the newspaper balls(lightly balled) in his tub to see if that will destress him enough to want to eat. You could always try a live fuzzy mouse overnight in his tub to see if that sparks an interest. He just may not have enough energy right now to digest that.

I hope this helps and I hope he does well for you. I can tell you have a great affection for this little strong-willed being.