When the hive started to slow in the summer, I probably would have gone in and checked to make sure they had a queen, brood, stores, etc. Perhaps you did check it out.
If it were my hive, I would be going through all the frames right now to see what is up. (do I have a queen, are they otherwise healthy)
If you find it is wax moth, I would remove any frames they have gotten into, then you need to crowd the bees down into one super or even a nuc so they can defend themselves. Sounds like you have to feed them also so they can build up.
Keep us informed, I am new at this also, but have dealt with the dreaded wax moths and saved my hive.