There are several things that can cause this.
* non food item in the stomach that he is unable to vomit up however in that case I would expect to see him vomit his food
* Intestinal parasites
* infection or irritation in the throat
* If coughing as well this may be associated with kennel cough.
. A spoonful of honey will help sooth the throat if that is the cause. Pepcid AC may help if he has an upset stomach. This can be dosed at 1- 10mg tablet per 40lbs of body weight every 12 hours.
The one thing I would like you to watch for is enlarging of the stomach. If the stomach become large and hard this could be a condition called bloat. Dry heaving is often one of the first signs we see.
Please read this information so you know what to watch for a bloat is a life threating condition.
If this is still going on tomorrow the he needs to be seen by a vet. If he show any signs of bloat he must be seen right away.
I hope all goes well, please reply back if you have additional questions or concerns