[kjc]

Shaking/shivering can come from the dog being painful, even intermittantly, and would be wise to have a vet look at him.

Some pups can sense impending storms and will become nervous.

Dogs will get chilled after a grooming if a lot of hair is cut off.

I could go on and on, but seeing a vet would be the safest thing to do. Maybe catch him on a video for the vet to see may help. Have his anal glands checked too.