When a dog cries when you walk past, it could mean anything, including wanting attention. If you have your large breed puppy caged with your other dog(s) walking by, then it might be crying out as in wanting to play and not being able to. By keeping the dogs apart you are ensuring that later on there will be behavior problems. In general if a dog is introduced to another when one or preferably both are puppies there are no problems. If the play gets too rough you might have to interceed. But over all they will sort out the dominance issues by themselves.

It is assumed you have by now decided on a dog food to feed the dog(s) involved, and only feed that one brand of dog food. If not then constantly changing the diet will make it more likely than once again you will encounter food allergy problems or like problems you experienced before. It's unclear why there is the need to give pumpkin frequently. A dog on a steady defined diet will self regulate itself. I can count on mine to deficate on their trips out at 9:30-10AM, and again after their larger meal at 4:00-4:30PM. Sometimes at 8AM. They may urinated up to 4X a day, again at almost predicted times. If they miss a bowel movement, that just means they do more the next time. A dog can be a finely tuned eating machine.

The answer your Vet gave you was a little flippet IMO. You should quiz the Vet about the dog's diet. If the Vet believes there is no problem there, but there is evidence of real constipation, then you should quiz the Vet about the possibility of Irritable Bowel Disease- which in itself has a myriad of causes.