there are alot of answers but these are the fastest and best ways i know use the bathroom it won't always work but it usually does, and if it doesnt, see if you have a fever or need to vomit stretch...
IMPROVED ANSWER: Though it may feel like you don't want to eat anything, try eating saltine crackers. They always help me to get rid of a stomach ache! Also, lie on your back and relax for a little...
If you do have medicine, use Pepto Bismo. It helps. If you don't have any medicine with you at the time, lay down and rub your tummy a lot. That helps me.
If you want to get rid of a bad stomach ache fast then: 1. lay down 2. rub your tummy for a little while 3. use the bathroom cause most of my stomach aches are from when i need to use the bathroom