From what you have told me, it appears that your dog has a mild digestive disturbance. This could be from something that was eaten or from some type of stress. The best thing to do for this is to fast your dog for 24 hrs. This allows the digestive tract to calm down and heal. Also, you can give Pepto Bismol at 1 teaspoon per 20 pounds every 8 hrs. After the fast, feed a meal of boiled chicken and rice. If the disturbance has resolved, wean your dog back onto the regular food over 2 days.
It is extremely important that if your dog continues to vomit during the fast, that you have your dog seen by a vet immediately. Even the dehydration will causes severe problems for your dog and this must be taken care of right away.
If your dog is still having difficulties, you will need a veterinary exam to be sure we have not missed something. This disturbance could be more severe such as an intestinal obstruction or other infectious agent or a pancreatitis.