It sounds like you are doing a great job but here are a few things to consider....
Misting - your cham would be better off with longer less frequent mistings. Its best to have the mister going for anywhere from 2 - 5 minutes 3 times a day and letting the cage get dry between mistings. The longer mistings will encourage him to drink.
Plants - take a look at the safe list here and get him some real plants they are great for some hiding and privacy and increase humidity and give him a place to get water as he can lick the leaves. I find the fake plants just absorb it and it doesnt run off to well.
Location- stupid pet shop. Chams like their privacy and he would probally be better in an area with less traffic, especially if he maybe unwell. I have a cham that tolerates people very well and he still likes his private home.
Feeding - are you only gutloading with spinach? Spinach is not a good gut load as it hinders the calcium absorption, try apples, oranges, collard greens, Kale, carrots.
I agree with Brad get him to the vet for a good check up and put your mind at rest. The raising Kitty blog is a great read... I have kept chams for about 5 years now and still pick up new stuff everytime I read it.
Keep us informed on how he goes...Good luck
