A dry, hacking cough that sounds like something might be stuck in the dog’s throat is one of the symptoms of Kennel Cough. Sometimes this cough is so hard that the dog will bring up white phlegm; also, coming in from outdoors (changes in environmental temps) may trigger a coughing outburst. He may sound like it, but vomiting really isn't likely to make him feel better.
Bordetella Bronchiseptica has an incubation period of 2 to 14 days. It’s often caught while dogs are boarded in kennels (hence the name) or even in dog obedience classes, dog parks, vet waiting rooms, etc..
This bacteria, in normal situations, isn’t especially difficult to treat. There is usually a secondary infection (or more) that needs to be addressed in order to eliminate the problem, so a vet check is warranted. The treatment is an antibiotic medication that may be given with a cough suppressant (a med that is prescribed )
Over the counter cough suppressants are not known to actually work in dogs or humans http://www.libertypost.org/cgi-bin/readart.cgi?ArtNum=124293
In dogs with immune system or other problems, this could be a more serious condition.
Other causes for dog coughing are environmental, like cigarette smoke exposure, dust, temperature extremes (too hot, too cold) and even stress. It could be tracheal disease or just allergies.
As mentioned, even though the cough suppressants aren’t known to really work, some people still recommend Robitussin DM .5 to 1 mg per pound. There are eye dropper/measuring delivery systems available for baby care in most pharmacy aisles of stores. They’re great to have on hand for pets.
Setting up a vaporizer (without medications in it) in the room with the dog may also prove helpful. Offering a heat source such as a heating pad set on low, beneath their bedding may make them more comfortable too; however, I prefer to avoid electric sources an animal may gnaw on. We use rice socks. Fill any clean sock ¾ of the way with uncooked rice and knot the end closed. Microwave this for 1 to 1 ½ minutes, shake it out to distribute the heat and make sure it’s not too hot - tuck it in the dog’s bedding - it stays warm and holds body heat for hours.
It’s very important to remember that these are just temporary, possible relief’s - in no way a cure. These will not make the animal ‘better’.
For more dog-cough information: http://www.canismajor.com/dog/cough.html
There are 9 types of vaccines available against Bordetellosis, usually products with whole cell bacterin, extracted cellular antigens or avirulent live culture. Some are intranasal (rather than injectable).
An interesting note is that among veterinarians, there is a differing opinion as to the necessity of these vaccinations, as well as how effective they actually are and whether or not the protection lasts. So even if you've had him vaccinated for this, he can still have it.
Columbia Animal Hospital provides more
You and your vet are doing the right things. With these extra options here, he should be able to get some comfort and rest, along with you. Hopefully you'll see the meds kick in and improvement by tomorrow.