Don't put it beside a window that gets a lot of sunlight! The inside of the tank can heat up to very high temperatures (think like the inside of a car).
What are you using as a heating device? I would recommend getting an Under Tank Heater (UTH) if you can - if not, a heat lamp will do. Just put it on one side of the tank and leave the cool side at room temperature.
He does look thin and dehydrated but it's good that he's eating and drinking. Make sure you are gut-loading and dusting your insects so he's getting all the vitamins/minerals he needs. Calcium is crucial! A moist hide might also help with getting him hydrated.
Good luck