Hi, noticed you are from Denver, we live in Adams county.. I hope meatball get better soon and you can figure it out once and for all what is causing him to get sick. Our dog is a Bullador, 3/4 eng. bulldog, 1/4 lab. He went through bouts of getting sick and we discovered his back legs were causing him so much pain. He didn't develop hip sockets so it was bone on bone when he walked. He was getting sick from the pain he was in.. I really hope your vet figures it out for you..