I have taken antihistamines, steroids and antibiotics.
X rays show nothing.
Obviously, you've seen a doctor. Go back to that doctor and ask to be thoroughly tested for a hidden infection. Warm steam soothes the irritated lining of the bronchial tubes, loosens secretions and promotes healing, and the aromatic herbs discourage secondary bacterial growth. An expectorant cough syrup might be of help. If that doesn't work, ask your doctor to prescribe a narcotic cough suppressant such as codeine .