A few years ago I had a cough with tons of mucous that lasted for weeks on end. I felt terrible and fatigued all the time. I picked up an old herbal remedy book (sorry, can't remember the name) and read about Lobelia as a fast expectorant for coughs. I think I took 1-2 doses of lobelia (whatever was recommended on the bottle), enough to make me start gagging. That's when the fun began. I then threw up a ton of mucous from deep down in my lungs, mucous that was not coming up from my coughing. Well, my coughing stopped within a day of that (not fun) cure. Lobelia is an intense herb for a desperate situation.
Last spring I got a dry cough that did not quit. Since it was a dry, irritated cough I went another route: I took elderberry extract 2 times a day and also made a strong batch of garlic tea (entire garlic cube boiled in water for 15 minutes) that I drank a small amount of throughout the day. I also went to bed every night sucking on a natural cough lozenge. It took a few days of these remedies but my cough went away about 2 days later.