I had a few colds in a series about a year ago. Since then, I constantly have a cough on and on, which is in sync with stuffiness in my nasopharynx. It is periodic. Half the time, I am completely normal, and half the time these symptoms appear. I saw a doctor three times about it, however, when I was in the doctor s office, I had no symptoms. I had a blood test, spirometry and an x-ray done to see if there was sinusitis or asthma. All were normal. I also feel some slightly bad taste or smell of the mucus that appear with the onset of the cough and postnasal drip. I had never felt any such taste or smell in my life before the onset of these symptoms about a year ago. The three doctors could not diagnose the problem. What tests should be done to determine if there may be an infection or if this is some allergic reaction or something else in addition to the tests I already mentioned above?