glass tanks are a bit hard for humidity (im talking from experience).
A water bowl with a larger surface can help. it will make the water evaporate more quickly and gets the humidity up. Or if u can make a hide with some sphangum moss (u can get it at a reptile store or so), even if u really want it now u can use a damp handkerchief or some like that in a hide so it raises the humidity in there,, it will help him