Honestly, there is the possibility that he could be sick, but I can't make that call. Handling him will stress him out. and really that enclosure is way to small you won't be able to achieve the proper temperature gradient in there, and if its glass I assume all the sides are see through? If they are he won't feel secure. I would also say humidity and the basking area are too low. Monitors need a much higher basking temperature than that, but with a cage that small the ambient will get too hot, so you have quite a few things going against you, and with him being so new that could be a factor as well.