If you look at the time, my post was only made a couple of minutes after your post with all the information in it...so I didn't see your information!
Since you have owned him only 3 weeks, if its your husbandry that's affecting him it would be things like lighting, temperatures, provision of water that need to be looked at although there are other things in your husbandry that you should look at as well. Carlton has pretty much covered the husbandry things that might be part of the problem. If its not solved by correcting those things then you need to look at things like parasites, history from his previous owner. Is he pooping lately? (I would be removing the substrate so that there is no chance of him ingesting it and becoming impacted.) He definitely shouldn't be sleeping during the day....and I would expect him to eat a bit more too. I would lower the basking temperatures to the mid to low 80's for now too. The UVB should not pass through glass or plastic, BTW.
Ice cubes are providing cold water and that could be a problem too...so I'm glad to hear that you are changing that.
Concerning gutloading..you can gutload crickets, locusts, superworms, roaches with a wide variety of greens (dandelions, kale, collards, endive, escarole, mustard greens, etc.) and veggies (carrots, squash, sweet potato, sweet red pepper, zucchini, celery leaves, etc.)
It important to dust at most feedings with a phos.-free calcium powder since most insects have a poor ratio of calcium to phos.
I dust twice a month with a phos.-free calcium/D3 powder to ensure that the chameleon gets some D3 without overdoing it. I leave it to produce the rest of the D3 it needs from its exposure to the UVB. D3 from supplements can build up in the system...but D3 produced from exposure to the UVB shouldn't as long as the chameleon can move in and out of the UVB.
I dust twice a month with a vitamin powder that contains a beta carotene (prOformed) source of vitamin A. Beta carotene won't build up in the system like prEformed vitamin A will, but there is controversy as to whether all/any chameleons can convert it...so some people give a little prEformed once in a while. Excess prEformed vitamin A may interfere with the D3 and lead to MBD..so be careful with it.
Hope this helps!