Strange bodies in the stomach or intestines of Dog
A bad sign are frequent vomits without feces deposition or scarce defecation; introduce carefully a thermometer, and see that instead of excrement, a viscous, glassy and consistent substance sticks to it. This indicates intestinal occlusion, caused always by the presence of strange bodies in the stomach or intestine. This may have been provoked by an intestine torsion (volvulus), an invagination or a tumor.
Important: Don't waste time! The animal condition will worsen quickly, and surgery, the only way to save him, will be more difficult.
Renal affections: The cause for frequent vomits may also be a serious renal affection. In that case, take him to the vet for a precise diagnostic. Waiting or using home remedies will only cause more trouble, perhaps the precise moment for treatment is gone. Solution is not to stop vomits, for instance with a suppository; the underlying disease is the one to attack.
In general, you can say that an occasional vomit is not alarming in, and can be normal. But if he vomits several times a day, an important disease may be present, so take him to the vet.
Leptospirosis: Constant vomits with general condition disturbances are ambiguous symptoms. We must think about leptospirosis even if the dog is vaccinated.