Do the Marjari Asana (Cat Stretch) to relax your back, enhance your digestion and relax your mind:

Steps to do it:
1. Get down on all fours and look straight ahead.
2. While you inhale, lift up your chin, tilt your head backwards, push your abdomen down and elevate your tailbone.
3. Hold this pose and take deep, long breaths.
4. While you exhale, let your chin drop to your chest, arch your back to the maximum extent possible and completely relax your buttocks.
5. Stay in this pose for a few seconds and then return to Step 1.
6. Continue with 4-5 rounds and relax.

Additional Reading:

Yoga Eases Low Back Pain

Yoga for Better Digestion

Yoga for Stress Relief

Pic Credit:  artofliving.org