Hi Susie,
Sorry to read about your coughing. Coughing can have many different reasons, some of them more serious. An often missed cause for chronic coughing is chronic sinusitis. There's more information on that here:
medicalnewstoday.com/articles/33188.php
I hope this may help you, best of luck.
Steven
Weird..I know medications have many uses..but my daughter used to take this one for migraines, I never knew it could be used for chronic cough as well. I thought it was an anti-depressant. ? I think you might need to get a second opinion for your cough..it could be serious..you know? Ask one more doctor:O)