Hi Kristin,

How has the little guy been doing? Is he still eating normally and active, but losing weight? Check out the Frog First Aid article: It could be parasites-

"Does eat, loses weight, listless.
Parasites in intestines, “Worms”
Treat with FENBENDAZOLE (PANACUR) 25mg/kg of bodyweight. Dissolve and drop on frogs’ back once a day for at least 10 days. Or dust the food items for 3 consecutive days."

The warmer weather could also effect frogs, mist more often, make sure the room is cooler, ect....

If he does not improve I would take him to a vet. Let us know how he is doing?

~Lesley