Lethargic kitty...

I am not sure what to think. I have two kitties, Steven and Moses. Moses is four months old and Steve is coming up on five months. Steve has always been energetic and eager to play, but Moses seems is weird. When we first got him at 5 weeks he was very playful for a week, then became a lethargic little one for about a month, then he transformed into superkitty with unreal energy and no inclinations towards us humans. Now it's a month later, and it's back to lethargic kitty, and he constantly needs to be near a human.

I am not sure what to make of it. He sleeps a ton, and Steve is obviously annoyed. He wants the old Moses back, or at least of his previous selves. What should I think? I am taking Moses to the vet this week, should I bring along a stool sample too?
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There's so many things that can effect kittens, especially if they weren't with their mother at such a young age. It could be a minor cold, or a parasite. I would also have at least one tested for feline leukemia and FIV. It would be a good idea to bring a stool sample in with you.