Yeah, they have a slow metabolism, so they don't do #2 as often as we do. I would get a digital thermometer to measure the temps and humidity. I see the little above the log, and they are way off. I bought some with my digital thermometer to to see, and they were anywhere from 10% to 15% off.
I would tell you to get rid of that heat lamp, but sounds like it gets pretty cool in that room. You could cover three sides of that aquarium with some foam boards (walmart lol) it would help keep it warm in there, and he would feel more secure.
Yeah, get that boy a rat. He should be able to take a med, but I would start with a small. It will be a big difference going from mouse to med rat.