Ask a Dog Vet and Get Answers to Your Dog Veterinary Questions
With this chronic vomiting, I would want to do an upper GI study. Endoscopy can be done to image the esophageal sphincter and the pylorus leaving the stomach. We can determine if there is an issue with a weak sphincter. We can also take biopsy samples at the same time to see if it's IBD (inflammatory bowel disease). This should give you a diagnosis and an idea on how to treat.
Treatment may be with pro-motility meds (Metoclopramide or Cisapride) if it's a sphincter or motility issue. If it's IBD, we use a hypo-allergenic diet and steroids (Prednisone) as needed.
I would have also started with Pepcid to see if that does the trick. If not, then moving on to scoping is the next step.
I hope this helps, let me know if you have any other questions.