Also Becki,
I read back through the thread, and see that you have an iSub tank. This tank has fully adjustable airflow, via a ring near the bottom of the tank that you can turn to close off the airflow. I mention this because it sounds like you directly lung inhale. If you are sensitive to either the PG or VG, I would recommend that you make the draw really tight, so that you can change the way you inhale. Because the particle size of the aerosol of the vapour you inhale, most of the absorption of nicotine takes place in the mouth, soft pallete, and throat. The size of the particles is too large to be effectively absorbed in the lungs, so I would recommend that you pull the vapour into your mouth first, take the vapour back into the back of your throat, not necessarily the lungs and then exhale. Also if you are having post-nasal drip from sinus problems, this would explain why your lungs are full of mucus, and I would recommend you use a sinus irrigation system - widely available from Boots the Chemist.