Have they run blood work? Pancreatitis can often be pin pointed in a blood panel. Pancreatits can be triggered by certain foods, even small amounts, I add this because you mentioned vomiting bouts after treats from your holistic pet store. Other signs to watch out for when you suspect pancreatitis is your dog not being able to get comfortable (pancreatitis is very painful), play bowing (which is actually the dog trying to relieve pressure from the pancreas, and no appetite. However, a blood panel can come back clear even if pancreatitis is the culprit. Sometimes it can take a couple of days for the enzymes to reach an abnormal reading.
I'm keeping your dog in my thoughts and hope that a diagnoses is reached quickly!