sad miniature schnauzer 18 months old adjusting to new home

I have just purchased a salt and pepper 18 month old miniature schnauzer from a reputable breeder, he seems very nervous and not used to home environment.
I know he must be missing brothers and sisters and mum but seems unusually nervous off his food at first but now eating ok.
He
just wants to sleep in basket and I have not even heard him bark yet. Is this normal, what is the adjusting period for a dog of this age or any tips you could give us.

We have had the vet look him over and he says he is fine but just traumatised. He just looks so sad any advice would be appreciated.