I have a cough lasting over 3 weeks now. I went through a course of zithromax 250mg, 1 tab a day for 5 days which did not help, then the doctor prescribed zyrtec - d for allergies, that has also not helped. My cough is productiive (with white phlegm), with a lot of crackling sound in my chest, however I don't have a fever or throat pain, please let me know - Ravi