The most common causes of cough of such long duration is smoking, other causes are postnasal drip, asthma and gastro-oesophageal reflux disease (GORD). Chronic cough not responding to treatment also often occurs after a viral infection.
Next Steps
Please get the following tests done
Blood tests - CBC to rule out infection,eosinophilia, ESR and Chest XRay
Medicine: Bronkolyte DC Syrup - 2 tea spoon 3 times for 5 days
Health Tips
If fever, weight loss or blood while coughing is there please consult a doctor