How long has it been going on?
How old is the dog? What breed?
Is it getting worse or just not better? Has a vet diagnosed it? What treatments have been tried and when?
True kennel cough virus lasts 3 weeks regardless of treatment. Severe coughing can last when the virus is gone due to irritation if the cough itself wasn't treated in the meantime. The antibiotics are to ward off secndary infections only, not to treat the kennel cough itself. (It's important for avoiding pneumonia, basically).
The cough can be controlled to lessen irritation by giving some Robittusin DM (no other variety) at a dose of 0.5 to 1.0 mg per pound of body weight (start with the lesser dose) no more than once every 12 hours. You can read about the drug here:
Controlling the cough this way should bring quick relief of the irritation. In the meantime, I would also only use a harness instead of regular collar with leash, as these breeds have many issues with tracheal irritation and collapsed tracheas as well; this only adds to the coughing!
Let me know if I can help further, and hope your dog is better in no time!