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It doesn't sound as though there's anything in the cage or room he's likely to be allergic to or anything that might cause the sneezing although it is possible that carefresh might be a problem so it is possible he has a cold, if he seems fine in himself, active, eating & drinking ok then I would just keep an eye on things for a few days & see if it stops, if not or if he shows any other signs of ill health then I would take him to the vet.
You don't need to clean anything other than pee for a while, they often store poo & eat some so you can leave that for a while & just let him settle.