I use both Pine and Aspen bedding. Be careful with the carefresh because if the chin eats it, it could cause blockage. The chin might be a little sensitive to the odor in the pine, mine have never had a problem though. The Aspen bedding, I have found, has the least amount of odor. I buy the Kaytee brand that specifically has no aroumatic oils.
Also, check the size of his poops. Are they tiny? large?
Start monitoring the amount of food and water being consumed. Don't fill the bowl up, put two tablespoons of pellets in there. It will help you see how much he eats. If he devours that, add another tablespoon. Make sure he has plenty of fresh hay, as well.
If he has been lathargic for a few days, you might want to take him to the vet to have him looked at. There are plenty of illnesses he could have already had that are just showing symptoms if you have only had him a week. Have his teeth checked for malocclussion.
You should do this immediately, for your protection. Most stores have a two week policy for you to find an illness in the animal and return it.
It could be as simple as the chin is just getting comfortable in his new surroundings, because sometimes that can be a lengthy process. It is always best to go with your gut. If you suspect that he is feeling ill, it is always best to be safe than sorry. Some illnesses can pop up suddenly and be devestating, and some come on slowly and cause a lot of pain.
Good luck! Keep us posted!!