I've been coughing for months, but chest X-ray was completely clear. What can I do?

Cough. Coughs lasting longer then a few months require a work up. Pulmonary evaluation would commonly include a pulmonary function test to look for evidence of asthma. Also, cough could be a sign of gastroesophageal reflux that would require medicine like prilosec. Additionally, we may order a ct scan of the chest. Finally, we review daily meds to see if you are experiencing a cough side effect.
See physician. .Common causes of coughing are post nasal drip, asthma and gastroesophageal reflux. Infections and chronic bronchitis are other causes. May need to have bronchoscophy or gastrointestinal evaluation for changes of gastroesophageal reflux,
Bronchoscopy. Should consult with a pulmonologist and possibly undergo a bronchoscopy to check your airways, which a chest x-ray would not be able to evaluate.