I am sorry to hear you are worried about Oliver. I am a veterinarian and will do my best to help.
There are dozens of reasons for a dog to not eat, and to vomit. It sounds like your vet has ruled out pancreatitis with a SNAP test, is that correct? Where any other blood tests, or an Xray done?
If you look at his gums, do they appear pale or are they a normal bright pink?
What anti emetics is he getting?
He could have liver disease, kidney disease, an intestinal infection, something blocking his intestines, inflammatory bowel disease, and the list could go on. If a blood panel and Xrays have not been done, that would be my next step if this were my own dog. If that has been already done, then I would next do an ultrasound; it shows many things that do not show up on Xrays.
It will help to know what medications he is getting, what color his gums are, if he has a fever. I hope to hear from you soon. Rebecca