I would think a titer test should have been done before giving him shots - he may have had some not long ago.
How about a heartworm check? Did they do that?
Is he on flea treatment?
Has he been neutered?
He has major changes in his short life. Drastic grooming cuts can affect some of them. He may feel naked.
I would try to coax him out of his "mood" by trying to play with him and offer him healthy treats for being a good boy.
The shaking is concerning. How much does he weigh? He may be having some issues with hypoglycemia. Do you have nutrical to give him?
The dr said he's healthy, but health isn't always obvious just by a visual check and blood work can tell a lot more.