I have bronchitis! what is it's cause and treatment usually?

Maybe antibiotics: You need to quit smoking if you do smoke. Your doctor may prescribe antibiotics. He may search for why you have it (?Allergies, etc).

Acute?: Assuming you are referring to acute bronchitis, the cause is usually either a viral or bacterial infection. If it is due to a virus, there is no specific therapy, only symptom management. If it is due to a bacterial infection, your doctor can prescribe antibiotics. For diagnosis and treatment, see your doctor. If you smoke, you need to quit to cut down on airway inflammation.