Are you dusting with calcium/D3 every other feeding and amphibian multivitamin once a week?

How are your temps in his tank?

They can tell when the seasons change and might be trying to hibernate. This is okay if they have a good nutritional status.

If his temps are low, trying warming one side of the tanks up to the mid 70's. This may keep him awake longer and make him hungry. It increases their metabolism.