Hi there...sorry to hear that your dog is unwell.
There are many different causes for vomiting. The most common cause is a gastritis/enteritis which is an upset intestinal tract usually resulting from a change in food or eating a new type of treat or table food.
The next possibility is that your dog has pancreatitis. It causes vomiting and sometimes diarrhea. Usually the front of the abdomen (just behind the ribs) is extremely painful in pancreatitis. The treatment for this disease is hospitalization with IV fluids and pain and anti-vomiting medicines.
The next possiblity is that your dog has swallowed an object that he shouldn't have causing an intestinal or stomach obstruction.
If your dog is not vaccinated, another possibility is parvo virus. This is more common in puppies, but can happen at any age. It usually causes great amounts of bloody diarrhea and vomiting.
It is also possible that your dog has a problem with his liver or kidneys as well which is a serious matter.
If your dog is still fairly bright and alert then you do not need to rush him in to the vet right away. You can try fasting him for 12-24 hours and then feeding a small amount of cooked chicken and rice. If he keeps this down then feed him this for a couple of days and then gradually mix in his regular food.
Some dogs with mild stomach upset will benefit from pepcid. If you would like to try this there is information on pros and cons and dosing found here:
If he is not bright then you can try giving him a small amount of pedialyte to get him through tonight and he should be seen in the morning. If you think he is extremely uncomfortable then an emergency visit is in order.
I hope this information helps! I will be online for a short while more. So, if you have more concerns about this question you can just hit reply. However, my baby will be waking up from her nap soon and I will be offline after that. If that happens I will respond when I come online again. Or, if my answer has been sufficient, please hit accept. Thanks!
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would highly advise contacting your regular veterinarian.