It's a little odd to begin coughing after having been vaping for some time. It's more common when you first begin vaping, as your body has to adapt from smoke to vapor. We all likely coughed when we first inhaled cigarette smoke until we adapted to it; the same is true with vapor.
Nicotine concentration, higher pg ratio, using too low resistance coils or too high voltage can also cause coughing. Specific flavoring agents can also cause some throat irritation.
Inhalation technique can cause coughing. In particular if you use a direct lung inhale. If you use a mouth inhale technique, you can allow the vapor a chance to cool in your mouth before inhaling into your lungs.
Using a longer drip tip can also help cool the vapor.
(Freudian Tip from Pink Spot Vapors and long drip tips from My Freedom Smokes.)
At times, after two years of full time vaping, I occassionally cough. I generally use higher resistance coils (2.5 - 3.0) on my regulated mods as I prefer a cooler vape.
