How big is the terrarium? Need more info to help you. What is the temperature of the room the enclosure is located in? Could be a simple fix of turning up the heat in the room. As far as humidity, have a large water bowl and put it on the hot side, that should help with humidity. if your terrarium has a screen top cover it with a piece of plexiglass, or a moist towel and you should be okay.

What kind of substrate are you using? Have you tried misting?