This is probably not a medical condition. Some dogs develop these types of traits as an obsessive compulsive disorder. A routine physical and a screening blood test should be done to rule out indications of medical problems that can lead to ravenous appetites, like diabetes and Cushing’s Disease. Unfortunately, even if just a compulsive disorder it may cause digestive problems like vomiting and constipation. If caused by anxiety, amitriptylline may give relief.