I've noticed over the day, and last night, that Fry hasn't sneezed at all, at least in the time he's been with me. During this time, he has had a bath and his change has had a super clean (toothbrush along the little nooks and crannys and bars and all! I looked like a crazy OCD cleaning lady), so I think there may have been something either on him or around his that was annoying him.
I changed to a less dusty hay today, I really didn't realise how many little particles came off the hay I was using until I got near the bottom of the bag and it was full of dust!