BLUE TONGUE SKINKS

My BTS northern gets up and just sits under his heat lamp most of the time he use to roam the cage a fair bit but now he is around his heat hide most of the time and ive been wondering if this is normal as they get bigger or is a problem with my set up or worse is he getting sick

Set up:
40 gal Breeder
Aspen bedding
1 WATER bowl
Fed wet dog food with veggies and fruit mixed into from the BTS Food chart from this site
2 Hides one under the basking area where he sits. the other on the cold
1 fake plant
1 night blub and bask spot combo No UVB because i read its not required if i add calcium powder and sometimes vit powder in his food
Temps used with Temp gun 91 under the basking spot to 78 in the cool side (AT night) at day its roughly around the same

He is a male Northen BTS and about 7 months old. Other then lazing about a lot lately the only odd thing is he doenst flick his lovely tongue as much anymore and isnt as jumpy if a i go into his tank. Any help is welcomed

Are you giving him calcium with D3 supplement?
This isn't really to do with your question, but it's important if you have no UVB to be using D3, as that helps them absorb their calcium and keep the risk of metabolic bone disease low.

Sounds like he is just getting used to his surroundings. If they are happy, they don't do much at all. If he is eating, drinking and looking fine you have nothing to worry about. Post a picture of your skink and setup.

And to add, I'd scrap the aspen. Gave my northerns nothing but shedding problems and excessive sneezing.

yea im swapping the aspen this weekend i dont even like the look of and to answer i am giving his D3 cal if every meal right now