Everyone has come up with very possible ailements that could be affecting you little guy. Uncle Chester has mentioned one I didn't think of and that is the frog trying to brumate. He is definitely right that waking them early can cause all kinds of problems. They can even go into shock and pass away, but that is near instant. Warm baths would bring him out of Brumation/hybernation. Especially electrolyte soaks.
One serious issue with hybernation is that if they try to do so on a full stomach the food will not digest due to a very slow metabolism and begin to rot in his gut causing him to become septic. Bloating is also caused by this sort of infection. Even so for something this bad a Vet is needed. I wish there was more help I could provide from here, but its difficult when you cannot see with your own eyes how the frog is behaving and the symptoms of what is ailing him.
Pleases keep us posted. I hope that he pulls through.