Welcome mate! A few notes:
1. If you're female, and unless your parents were especially cruel you probably are, you may want to change your name. This should get you sorted:
http://www.e-cigarette-forum.com/fo...ed-my-real-name-how-get-user-name-change.html
2. Many stores will label or allow you to choose what blend of PG/VG you are using, referenced as 50/50 (50% of each) or 80/20, etc. PG is usually listed first, but not always. Some don't as they consider it a trade secret, but it's mostly marketing mystique.
3. Before we go into PG/VG for your stomach ache which is very rare, it's probably best to make sure your technique is OK so you aren't gulping air and such.

Robino1 explains this the best, but I'm not allowed to ask her to do it anymore, especially not slower and in greater detail.
This link will give you some tips, as you generally don't inhale as you would with a regular cig:
http://www.e-cigarette-forum.com/forum/ecf-library/337017-inhalation-technique-e-cigarette.html