Suggest Treatment For Persistent Coughs And Breathing Issues

I have been caughing for more than 3 weeks now and I don t know what is the cause of it and how I can cure it. It comes at random times. My throught is irretated and makes me caugh. Sometimes it is so strong that I feel like I cannot breath or might vomite. It particularly bothers me when sleeping. Could you please give me some guidance?