kitten 645 beat me to it, I was going to say its probably a URI too! Did you get him from a shelter or has he been around other cats likes strays before you got him? I know you just added Gigi to your household too, hopefully she won't get it too. Kittens do get sick more often than older cats who have been immunized, has he been to the vets yet for shots? I would call his vet anyway to check if you need to do anything to make him more comfortable at least.