He looks dehydrated to me (collapsed casque). From your description you don't really know how dry your cage is getting between mistings. Do you have a humidity gauge? Not the little pet shop analog type...they are terrible. Get a decent digital type at a home improvement store. I would bet your cage is a lot drier than you realize for much of the day. Chams lose a lot of body moisture through respiration in dry air. If he was well hydrated he would not be drinking every time you spray (3 times a day), he would not try to drink out of the dripper tub, and his casque would be full and fat looking.
Some things to do right now:
Get the humidity gauge (hygrometer).
Add live plants to his cage to offer more surfaces for evaporation.
You can safely cover part of the cage with plastic sheeting to hold in some moisture.
Mist for longer periods (2 minutes is not very long) or start misting, wait for him to start reflex swallowing, and gently spray over his head so the water drips down his face. He may start licking and swallowing this way too. Keep spritzing until he tips his head up and turns away from the water. Chams have small stomachs and can't "store" a lot of water at any one time.
Try using a room humidifier aimed right into the cage. Run it in cycles controlled by a lamp timer.