What Is The Cause And Treatment For Severe Cough?

Ive had a cough for the last 9 weeks that has progressively gotten worse. My doctor keeps putting it off as a seasonal issue but when I went to the urgent care I was diagnosed with Bronchitis and Flu B. they gave me an antibiotic and steroid shot. this cleared up the fever and many other symptoms but I still have a bad hacking cough with white foamy phlegm and crackling and wheezing mostly when I lay down at night.