If blood work and X-ray are normal but cough persists, swollen adenoids are a common cause. An anti-allergen and steroid-based nasal spray typically resolves it within 2 weeks. Acid reflux is another possibility — avoiding certain foods and waiting 2-3 hours after dinner before lying down helps. Dry weather and changing seasons can also trigger prolonged coughs. A humidifier running through the night provides relief. If cough is only at night, it is likely post-nasal drip. Consult your paediatrician if it exceeds 3 weeks.