Surprised no one has mentioned Chytrid yet...
I'm going to go out on a limb and say he bought it in a petstore.To those who don't know, that means it is pretty much wild caught and has a massive chance of having this fungus.
Tons of info online about it man, read up, read some of the signs and symptoms.Also read how bad it is for Amphibians.
The uva/uvb is super important as well.It lets their bones form proper and also lets them utilize their food better.Your pacman will die just as horrible and just as slow pretty much as it would from fungus if you neglect it UV rays.UVB specifically if budget is a problem, but UVB is the main one.I like to give both, as they evolved under the sun...which has both.
That important.
As for food, look for those fat green feeder worms most petstores that sell live food would have.They are called horned worms, stop with the goldfish.
The occasional rat/mouse and insects...bait shop/wal-mart nightcrawlers are really good as well.I'd grab a few like spaghetti with feeding tongs, and as soon as it would see the movement I'd be trying to pry the tongs out of it's mouth.Over shot the bite EVERY time!Typical lunger...
Form what you said this is pretty reversible IF, IF, IF, IF, it is not trying to Aestivate (hibernate).
If you've always had him relatively cold he might be so darned confused...
Also research MBD, causes and effects.
Good luck man, I love my frogs!