Pancreatitis is very common in yorkies. I am sure there will be a bunch of posts in a little while about it.
For now, here are a couple of links so you can read a bit about it:
Pancreatitis (Inflammation) in Dogs Pancreatitis - Learn about signs, treatment and prevention of pancreatitis in dogs and cats
Hope all goes well at the vet. If it is pancreatitis, he will more than likely need a few days of IV fluids.