1 year old doberman puppy chronic loose stools. Vets tested for multiple things.?

I need help. Vets can not determine what is wrong with my 1 year old Fawn Doberman. He has chronic loose stools. Multiple blood tests. first two didn't show anything out of the ordinary. This last one done by an internist says B12 way down, and other pancreatic enzymes are down. Wants him started on weekly B12 shots. Internist says he IS NOT presenting most of the symptoms of pacreatis.... any other ideas? He is a wonderful dog and belongs to my 15 year old daughter. Eats well, does not vomit, drinks water, but chronic loose stools... and if he exercises at all stools become more loose...