Lingering dry cough after a cold

My boyfriend caught a cold last winter and then had a lingering dry cough for 3-4 months which eventualyl went away.  He caught a cold again last month and the lingering cough is back again.  He has no phlegm, or other pain, dizziness etc.  He says his chest feels slight tight but only very slightly and that makes him want to cough.  He gets coughing attacks for a few seconds or few minutes at random times throughout the day and night.

No history of allergies etc.

Any ideas?

[National Jewish Health]

Your boyfriend may have asthma that can present with cough and/or wheeze, often worsened by a cold or episode of bronchitis.  His "tightness of the chest" would be consistent with the diagnosis of asthma.  Postnasal drip, that may persist long after a cold has resolved, is another cause of chronic cough.