Judging from the symptoms that you're explaining and the setup that you've told us about so far, I would have to go out on a limb and say you're probably using 20 long with a screen lid and heat bulb. The screen lid and heat bulb are your problem. Your best bet would be to get an under the cage heater and a thermostat. If you cannot afford to buy a handful of moss I don't know how you can justify a pet.