Alright, that's something we can check off the list.
Try looking for API Stress Coat+. It's one of the better water conditioners out there and is also a stress reliever and can make your fish feel better. WalMart doesn't sell it but you can get it at PetSmart, PetCo and you should be able to find it at your local fish store.
You said he hasn't eaten, you can try getting him some frozen brine shrimp or glassworms, maybe even frozen blood worms. Thaw it out and try feeding him some, it may coax him to eat some since it's more appealing then flakes or pellets.
Have you been able to see any of his poo at all? If so, and if it's stringy then he may have an internal parasite.
You should also look for (if you don't have them already) Aquarium Salt and Epsome Salt. Epsome salt you can get at Walgreens or any type of drug store. The Epsome Salt will need to be used if he has internal parasites or if he ever gets bloated. Aquarium salt is mainly used for external problems but it may help him out as many fish bounce back when being treated with it.