What Causes Chronic Cough And Nasal Congestion?

On feb 23 went to the dr with congestion and nasal drip infection. dr gave me azithromycin to take 2 the first day 1 for 4 days wait two days and take 1 every other day for one week. For the2 weeks of medication and did not have a mucus coughed up, the third week I was fine but the 4th week it came back with a lot of hacking cough with very little mucus, I can hear the mucus when I exhale and inhale very loud should I be concern