I Have Had This Horrible Cough For 4 Weeks That

I have had this horrible cough for 4 weeks that has settled in my chest. After 3 weeks I saw my physician who prescribed an antibiotic as said I had a sinus infection and the start of bronchial pneumonia. I actually am feeling worse now, cough up a lot of productive phlegm, so now wondering if it isn't a viral thing I have or if I need to be concerned something else is going on? I am extremely tired and achy, but do not seem to be running a temp. My husband thinks it is just a virus that has to fun it's course. I've been drinking lots of water and also have gone through 2 bottles of cough syrup, which seems to help me sleep at night; also my appetite has still been good. Is it common for this to be going on as long as it is??