Hey kingslothdrops... Congratulations on making the switch before anything else.
With regards to your question, another thing which may contribute to the chest pains aside from the withdrawal symptoms of quitting tobacco is the nicotine density on your ejuice. A large dosage of nicotine in a short span of time may cause temporary broncho and vaso constriction. If you are experiencing chest pains during heavy vaping, just go ahead and give it a break for 30 minutes or so and drink a glass of water while you're at it.
I think almost everyone here has experienced the same problem especially during the first few days or weeks of making the switch to ecigs. With all the amusement of finally finding an alternative to tobacco, it is normal that we vape practically constantly throughout the day(I know I did) thus causing you to consume more nicotine than usual. Nicotine is metabolized pretty quickly though so a quick vape break every now and then should do the trick.
Don't worry about the "water vapor build-up in your lungs" theory though. It's simply not true. Hehehe
Hope this helps. Vape on buddy.