The most common causes of a persistent cough in a non-smoker with clear lungs and a normal chest X-ray are:
- Post-nasal drip
- Occult asthma
- Acid reflux
I suspect your doctor asked you about related symptoms, such as nasal congestion, wheezing or heartburn. You probably said no to these symptoms.
Some people with asthma cough, but dont have any audible wheezing. So it makes sense that your doctor prescribed an inhaler even if he or she could not hear any wheezing on your exam.
Based on your symptoms of increased cough after eating and at bedtime, esophageal reflux would be at the top of my list. Acid from the stomach can wash back into the esophagus. It then tends to move up higher to the throat. This irritates the tissue and prompts coughing.
Symptoms of reflux often happen when lying down and after meals. Many people with reflux will not experience heartburn or indigestion, and cough may be the only symptom.
Post-nasal drip may be due to allergies, prolonged congestion after a cold, or a sinus infection.
Occult asthma means that the wheezing is not obvious and cough may predominate.
Other causes of a prolonged cough include:
- Some medicines (especially ACE inhibitors like captopril, lisinopril, and enalapril)
- Hypersensitive bronchial tubes following an upper respiratory infection
If the cough is secondary to acid reflux, then treatment would consist of:
- Not lying down for three hours after eating
- Eating smaller meals
- Noting which foods make the symptoms worse, and avoiding them
- Acid blockers including proton pump inhibitors such as omeprazole or H2 blockers like ranitidine
If the persistent cough is due to post-nasal drip, then decongestants and antihistamines should help.
For occult asthma, a prescription inhaler would be advised.