Help-I dont think chip is well :(

[belle3.]

Its hard too explain-but i just know chip isn't well, he not his usual self, he used too constantly run on his wheel run around his toys & have fun now hes always in his house asleep-ive seen him drink (lots) and eat some mealworms i picked him up yesterday to check his behind and he's totally clean so its not wet tail
i havn't changed his diet or tried a new treat? i have no idea whats up?, it has been colder than usual at night in my room but not too cold all of my other hamsters are fine?, i dont know if i'm just worrying over nothing but i am really scared he could be ill, can someone help or give advice?xx

[Gillzy]

How old is he? Hams often slow down in their old age. Might just be that?

[belle3.]

Sorry-i forgot too put that in:/xx
hes still quite young? ive only had him since about may (for my birthday)
hes only a little hamster?xx

[fluffymunchkins]

Has he lost any weight?
How does he look in himself?