Sounds to me like a specialist is in order. While initially the cost might seem like a lot, often they can get to the bottom of things quicker and in the end save money.
I would not advise you on the food...you have a pup with pancreatitis and diabetes and he needs a very careful diet. Personally, I would, at some point, probably do a nutrition consult....BUT first things first. Try a specialist .... or a vet school if there is one close to you???
You can find an internal medicine specialist here:
American College of Veterinary Internal Medicine > Home
Look for SAIM (small animal internal medicine)
Please keep us posted.