oh the good old lower back pain. its horrible isnt it.. um when im sitting i like to sit a pillow in the curve of my back, seems to help. When laying on ur back in bed put a couple of pillows under ur knees or put one under ur back. If all else fails get ur DP to give that area a light massage while ur sitting on the edge of the bed....
For exercises, try some swimming or yoga. For stretchs, stand up straight and twist the top half of our body a little around to ur back, using ur arms..this seems to help my back to stretch out a little.
All else fails, try using a heat pack and put it in the pillow that u have behind ur back.

HTH xox