Is he fully vaccinated?
OK, thanks for your reply. I would suggest having him seen by a veterinarian in order to have his abdomen x-rayed to look for signs of a blockage, which is common in young dogs, as a result of swallowing foreign objects. Without treatment, continuted vomiting can cause severe dehydration, weakness, and even death. Shaking can be a sign of pain, or weakness.
Please let me know if you need more information.