Does he have any sort of build-up around the corners of his mouth? if he has mites that's a typical sign. It'll look like the same type of build-up as when a little kid gets Oreo crumbs in the corner of their mouth. You can take a moist paper towel and wipe the corners of his mouth and if there's residue, then I'd treat for mites. Secondly - you can check for mites in the water dish. When snakes have mites, they soak themselves which causes them to let go and *hopefully* drown in the water. You can find dead mites floating around in the water too.