I just finished a z-pak but still am congested and have green phlegm ....how long will these symptom last? When I went on the antibiotic, I had a horrible sore throat ( strep culture negative) which kept getting worse and only some congestion. After starting the z-pak, I became congested and started producing green phlegm. The z-pak got rid of the sore throat. I am sure it was some sort of bacterial infection . Is it possible that it morphed into something else? Should I get another round of the z-pak?