If you can indicate "his" weight it would be helpful too.
At 12 weeks old
Peppa was 61g
Toothless was 51g
Rex was 51g (she grew to 630g full grown) and Puff was 43g (he grew to 640g full grown).
Is very likely "he's" the runt of the litter (not a bad thing in itself, I've had a runt (a bluetongue skink) who was a bit smaller than his tub mates (all siblings) who grew up big and healthy and is uberaffectionate (George : he chose me , came over to me and actually looked up at me as if to say "pick me ! pick me PLEASE !" and he then proceeded to crawl onto my hand and I fell in love immediately and had to take him too , only planned on buying one , his sister, walked away from breeder's place with 2 baby bluetongues).
Being smaller than "his" tub / tank mates / siblings / clutchmates will mean "he" was likely at the bottom of the pecking order and only got the scraps of food, and hardly ever got a live insect, and only got the worse sleeping spots , and likely never got access to the prime basking spot, and was intimidated and under constant stress while with the other hatchlings, he should have been separated by the shop and put into a tub / tank by himself but they likely wouldn't care or even know and left "him" to own devices .... result, stunted growth and maybe some malnutrition , both fixable since you got "him" very young.
Give him a few days to a week to settle in (he'll be suffering relocation stress) and keep offering live insects (small crickets or roaches or calciworms (phoenix worms) or small silkworms at least 2 times per day, 3x per is better at his age, just a few at a time so "he's " not overwhelmed by bugs running in all directions, and start offering some grated carrot mixed with a high calcium green leafy vegs (cut up roughly) , and let him get used to you by keeping the handling to minimum for now , spend lots of time close by and talk to him frequently, and maybe pet him when he's basking and relaxed.
He'll come good in short order.