Okay here's the thing. My 4-5 month old turtle, Poky, isn't really eating for the past 4-5 days. He's in a 60 gallon tank with 2 other turtles(Moky and Choky) who are younger by a month. When I put food in the tank, Moky and Choky run for the food but Poky goes slowly to the food and tries to eat it. In the past, he was fully able to swallow the pellets in one gulp but now, it's almost as if he's lazy. Now, he tries to eat it but he can't and then he gives up. I try feeding by hand but it doesn't work, he completely ignores the food. He's usually on the basking area and doesn't really budge when I come in, unlike Moky and Choky who immediately jump off once they see me.
So... what could be the problem? It's almost winter time and I don't want anything going wrong.

Oh yeah, Poky likes to sleep alot.