Coughs come from lots of things. Coughs at night can be due to post-nasal drip irritating and drying out the back of your throat and esophagus. That particular problem tends to be worst in spring & fall (pollen in spring, moldy fallen leaves in autumn; mowed grass can also be a problem in summer). I use Allegra* at those times to help dry out the sinuses and stop the post-nasal drip. Then you also can get coughs in winter from lack of humidity in heated air in houses in the north or from dry, dusty air in summer in the south.
When cough drops and medicines aren’t working, here’s a quick low-tech, all-natural fix: Steam your throat and lungs.
Make a megaphone out of a cardboard folder with a mouth-sized hole at the top. Then boil water in a tea kettle with the burner on high; once the water is boiling, take off the top of the tea kettle and turn the burner down to medium-high; put the megaphone over the top of the kettle, and breath the hot, steamy air. It may cause you to cough up some phlegm at first, but keep breathing the steam for about 5-10 minutes at a sitting. Don't fry your mouth and lungs with the steam, but try to make the steam as hot and thick as you can stand it. It's great for moistening and soothing the back of your throat, esophagus, and your lungs.
Try this at bedtime and then again whenever the cough wakes you at night. If it helps out, then do it once in the morning each day during spring and fall just to keep the back of your throat and your lungs moist and healthy.
I steam my lungs whenever I have one of those real bad deep-seated chest colds during flu season, and it’s the only thing that allows me to get a few hours of peaceful rest. And then I also steam my lungs occasionally in spring and fall to ward off allergy-related coughs. (I’m an ex-smoker.)
* Personally I prefer Allegra (generic: fexofenadine hydrochloride) over Zyrtec or Claritin because Allegra works great without making me feel stoned or jittery.