[cypher]

The cage does look a bit small, the substrate doesn't look very deep, with most barred cages if you fill the base completely the depth will be just about enough, any less than that doesn't really give them enough to dig, burrow or make a proper nest really.
What kind of house does he have, I can't make it out. A Syrian does need quite a large house, maybe shoebox sort of size, it's important the house has no base & is sitting on top of the substrate so they can dig in below. The other things you have in there look ok but just making some small changes like the substrate & house may help make him feel more settled.
With this kind of sized cage it is difficult to have deep substrate & fit the wheel in, you may be able to fence off an area with bendy bridges for the wheel & have more substrate in the rest of the cage unless you want to look into getting a larger cage for him.