Try to tempt him with some fresh greens dipped in water. Fragrant herbs are often the best thing to spark an appetite in a bun. Parsley, cilantro, fresh mint, dill. Hydration is important, hence the dipping the greens in water before serving them to him.
You can give him baby gas drops (simethicone) in case he has gas. Gas can make a bunny stop wanting to eat. Simethicone might also help lubricate the GI canal so intestinal contents can slip through easier. It’s not absorbed by the body and can be given on suspicion of gas according both to Medirabbit and Dana Krempels. Many of us here swear by it.
It’s of course great that he’s moving around. Clean out his litter box so you can keep track of his poop. If there’s really few poop or if he declines in some other way, you need to take him to a vet. A bunny not eating can become critical very soon. Do not wait more than 8-12 hours before seeing a vet if he’s not eating or pooping.
Is his ears cold he might need some warming up, although if he’s moving around normally he probably is keeping warm. If you have a thermometer you can try and take his temp like in this excellent video by Mary S Cotter:
http://www.howcast.com/videos/514693-how-to-take-a-rabbits-temperature-pet-rabbits/
Sick bunnies often get hypothermic, so that’s sth to watch out for.