Help - My chinchilla is acting strange and is over grooming himself?!

My chinchilla Buddy is chewing his fur under his chest. I can't tell if he's pulling it out or not as he's just started to do it. He seems irritated and not himself meaning he's acting very frustrated and irritated (chewing his cage which he doesn't normally do and avoiding coming out for exercise) and is constantly grooming and chewing or licking his chest in particular. I've just come back from holiday so can it be stress because I was away? Please help, I need some advice he has never done this before and he is 4 years old.