Your hedgehog shouldn't have any light on night, that's probably why he's never been really active. A Ceramic Heat Emmiter, CHE, only emits heat, no light. Depending on your cage set up a 100 watt is the best way to go with a 8.5 to 10 in dome. With your little guy being older, he is much more susceptible to the cold and to infections. He will need to be kept warmer than before and steadier than before if he is to get better. I can't help you with his sickness but a change in heat source and no light at night will definitely help your little man.