Cronic Cough, 17 months?

What is the reason for this cough. Could it have anything to do with his stomach because whenever he coughs a lot he burps. He also throws up a lot. His stomach is sensitive. He can't eat a lot of food, and certain types of foods. He used to smoke but stopped 17 months ago and that is when he got this cough. He had it but it wasn't this bad. it was a small cough. The cough he has right now is dry. No mucus comes out when he coughs. He feels his chest to his throat is all dry. sometimes the cough lasts a couple of days straight. he has tried nose sprays recomended by doctors but they don't work. He has been tested for bronchitis and the doctor says his lungs are clean and good. the doctor said that he doesn't have bronchitis. He also tested for alergies and he does not have any. He tested for gerd as well and he doesn't have gerd. he's 57 years old and it has been going on for 17 months. sometimes he can't breathe. Please, please help. Thank you to all suggestions and advice.