Why a cough lingers
A little coughing is normal; a lingering cough not so much so. See your doc!
Four weeks ago you were felled by (for lack of a more specific diagnosis) the dreaded flu. For three full days you suffered the attendant aches and pains, sniffing, coughing, moans and groans. By day four, you were pretty much fully recovered -- except for that darned lingering cough, which, weeks after the fact, is still keeping you company and making life miserable for you.
Coughing every now and then is normal. A cough is caused by secretions from your lungs, which prevents infections, which means that it is a good and helpful cough. It is also normal to cough when we are trying to clear foreign substances from our throat. However, a lingering cough that refuses to go away is not normal.
It is not unusual for a cough to hang around long after the symptoms of the flu, a cold, pneumonia or any infection that involves the upper respiratory tract has been treated and ostensibly cured. It is possible that the infection is still lingering or it may be that the infection is truly gone but your respiratory tract remains inflamed, which makes it especially vulnerable to irritants, which results in the lingering cough.
That lingering cough may be the result of bronchitis, which manifests itself in coughing, that produces mucus. If your mucus is yellowish green you probably have a bacterial infection. You may also find yourself wheezing.
If you have problems with your sinuses and are experiencing drainage down your throat, this can cause a cough that probably will not go away until you get your sinus situation resolved. Generally, we swallow mucus that comes from the glands in our sinuses, nose and throat. This mucus moisturizes and cleanses the nasal passage. When you have too much sinus discharge it will accumulate in the back of your throat. This is called post nasal drip. It triggers your cough reflex. If your sinus condition is producing way too much mucus your cough is more than likely to become bad.
Gastroesophageal reflux disease or GERD can make you cough. When stomach acids flow back into the esophagus, which is the tube that connects your throat and stomach, this irritates your throat and esophagus as well as your lungs and causes coughing.
Many of you may not know this but blood pressure drugs can result in a lingering cough. Angiotensin-converting enzyme (ACE) inhibitors are notorious for causing a bad cough among 20 percent of those who take this type of drug. Usually, the coughing starts up about a week after taking ACE; however, it is possible that the cough will not appear until six months later. The cough generally goes away after a few days but sometimes it lingers.
If you have had pneumonia it is possible for bronchiectasis to develop afterward. This is a chronic lung condition, which results in the aberrant widening of your bronchial tubes. When this occurs, the tubes are unable to clear mucus from your lungs, which makes you cough. You may cough up blood or sputum that is discolored.
Those who are plagued by asthma may experience a lingering cough, which may come and go depending on the season. The coughing may get worse when an individual is exposed to certain fragrances or chemicals or to cold air. When a lingering cough accompanies asthma it is referred to as "hyperactive airways disease."
If your lingering cough persists, see your doctor. Seek immediate medical attention for a cough that is accompanied by chest pain or other symptoms, particularly if the mucus is thick and greenish and smells bad or you are coughing up blood.
MayoClinic.com: chronic cough
National Institute for Health