Welcome to ecf! You've been given great advice, here, and I'm glad it's helping. Try to remember that you didn't go from zero cigs a day to a pack a day in one or two days. It took a little while. Same thing with reducing nicotine: it takes awhile for your body to adjust. Nicotine is a stimulant, and without it, you will be tired, grouchy, and just feel badly. Slow and steady, and you'll get there.
As far as your lungs hurting, that's probably not related to reducing nicotine. Your lungs are damaged from smoking and will take time to heal. Finding the right mix of PG/VG should help, as will drinking a lot of water. If you still hurt after a few weeks, see a doctor. Please. Better to be safe!