Chronic cough may be caused by allergy or sinusitis resulting from a post-nasal drip. Chest infection and asthma are the other causes.
A persistent cough is not normal and needs to be evaluated by a doctor. In the event where all the routine tests were not helpful; allergy workup, in particular, food allergy may reveal the cause.
To get an accurate assessment of your chronic cough or persistent cough condition, you can consult the Singapore ENT Specialist Dr. YT Pang at the Centre for Ear Nose Throat Allergy & Snoring (CENTAS).