Re: stomach problems:

yep, having the spine out of whack affects digestion too.

Basic stretches are always helpful - hurdlers for instance. Or put both legs out straight while sitting, relax the knees, grab the feet and pull so that the stretch is in the back not the legs.

Lie flat, bring your right leg over to the left, this is a sideways/twist spine stretch. Do both sides.

The plow position - from your back, take your legs over and behind your head. Keep legs straight, toes touching the ground, then bend the legs and relax. Roll out slowly.

Here is a link to the Salute to the Sun, a Yoga exercise that stretches every muscle and the spine:

http://www.geocities.com/Athens/Ithaca/9012/salute_to_the_sun.htm