Since he's young and presumably growing, it's also possible that the prey size that used to keep him satisfied for awhile doesn't last him as long and it's time to bump it up. Sometimes you don't notice how much your young'uns are growing when you see them every day until suddenly they're borrowing your clothes and cramming for the SAT.

Could also be that he's getting more comfortable in his environment and coming out to hunt more. Although I agree with others that your hot side is probably too hot, especially in a relatively small space; and during the day it may be even hotter than you think if the tank also gets more sunlight in the window this time of year or your house heats up in the afternoon. A thermostat should take care of that - if you don't have one, you should in any case.