Hi there...
At 9.5 weeks old (and for a few months ahead), he is still just a new baby (like human babies), he will sleep quite often. Plus he is on antib's which are probably making him more sleepy. Keep him warm and follow the Vet orders.
Children's Vanilla Pedisure (w/fiber) is good to have on hand, when he won't eat. Most Yorkies love the taste. It has protein and nutrients
What food are you feeding him?