Join Date: Jun 2008
Location: northern Minnesota
How are his eliminations? If he has diarrhea, that can very quickly and severely dehydrate a kitten.
You're not giving him any dairy products, right? No milk, cheese, yogurt, etc.? Many felines are lactose intolerant and can't handle dairy products made from cow's milk. If that was the case, though, he would have diarrhea.
Dehydration can be very serious in a kitten, so I'd recommend mixing warm water into his food, or, if you're feeding kibble, soak it in hot water until it's taken up as much water as it can absorb. That'll help put some more fluid into his system.
It sounds like it's time for a vet check with your regular vet, too.