Actually, PRAA, "Persistant Right Aortic Arch". Also look in to Canine Megaesophagus.

First, I am so sorry that your baby is having difficulties. Is he vomiting (which involves retching food from the stomach using abdominal muscles) or just regurgitating (bringing undigested food back up after swallowing it). If he is regurgitating undigested food, water or mucus, I worry about persistent aortic arch, which occurs because of a glitch in development. Puppies will not outgrow this disorder but it can be corrected with surgery. In case this is the problem, please contact your vet immediately because your puppy may need help immediately to avoid further damage.

mega-esophagus?

ME He was doing very poorly in spite of all efforts to put on a little weight. Even with proper positioning for 15 minutes after each meal or drink, he failed to gain. I had to let him go. Very sad here today.

So sorry to hear about the loss of your puppy. I had the same situation, which is why I recognized the symptoms, and lost my puppy at 9 weeks old. It's one of the reasons this is called a "heartbreak hobby".