If you dog should happen to have pancreatitis then administering food of any type will make the situation worse. Hopefully your Vet will check the levels of the various enzymes produced by the pancreas.

If the pancreatic enzyme levels check out ok, then there is the possibility of other metabolic problems such as Addison's disease, or something more simple as parasitic (e.g. worms) infection in the intestine. It could also be caused by digestive enzyme insufficiency, or the catch all IBD. For the later cases you can ask your Vet to prescribe Metronidazole to help with the diarrhea, and Zofran for the nausea. But again until Pancreatitis is ruled out, the dog should not be encouraged to eat.