13yr old son, croupy cough for three weeks also has mucous on amox/clav, prednisone, Bromfed dm, xopenex (levalbuterol) but no major improvemnet can this be pnemoni?

Unlikely. The fact that the cough is croupy indicates that the vocal cords are involved. However, given the lack of response to a multitude of treatments makes me wonder if the cough could be whooping cough. Obviously your son has seen a physician, but i would suggest the possibility of whooping cough. The diagnosis can be made by checking pertussis antibody titers.
BRONCHIAL ASTHMA. A chest x-ray will rule out pneumonia .Advair, Dulera or symbicort (budesonide and formoterol) should be added to the regimen aside from the oral prednisone. Environmental factors are also important to control.
Prob not. If it's a viral infection, none of what you mentioned will help. It could be pertussis, which if in the cough stage again none of the above will help. At 13 your child is high risk for pertussis. Usually it will run it's course, but he could be a risk for small children and the elderly. There are some viruses that can cause a pertussis-like illness. Sinus inf possible, but antibiotic should help.