Hi, I had the flu on December 7th through the 17th. I coughed after that, so the doc prescribed me a Z-pack which I took. She said the X-ray didn't show bronchitis, but to be safe she would give the antibiotic. It seemed to help, but now the cough and phlegm returned. It is sometimes clear and sometimes yellow. I walked in the cool weather and that seemed to bother me,as I started to cough. Any idea what the problem is? I have anxiety and some times get scared of the worst. I keep thinking it's lung cancer. Please help.