What parasites was he treated for?
If it was coccidia, and he was treaded with Albon, you might want to read this and print a copy off to take to your vet's next time you see him.
Yellow Fungus - Cause & Effects
Up until recently, we've been treating ours with the Essential Probiotics from Nature Zone, mixed with a couple of other supplements.
We recently found a product called "AcidophiLiz", which contains all the things we were mixing together ourselves. It comes in liquid form an has an eye-dropper built into the cap for feeding.
The Nutribac & Probiotics you can sprinkle on their veggies & crickets, but if they're not eating too good, they're not getting all the supplements they need. Most dragons, even if not eating great, will take liquids from a dropper though, so it might be something you want to look into.
-----
Axe
The Reptile Rooms