Bronchial irritation of some type, perhaps with obstruction.
Some type of chronic infection (e.g., tuberculosis) might also be a consideration.
Bronchial irritation can produce a chronic cough and can occur as a result of a
foreign body in the bronchus, a chronic infection in or near a bronchus, or a tumor
in or near a bronchus. A six month history is relatively acute and the progressive
nature of the dyspnea suggests a developing problem.