You might want to get a small pillow or roll a small towel up and use it behind your back to support the lumbar curve. Also, take a small towel, roll it and place it along the outside of your driving leg. Sometimes when driving more than a short distance, the leg automatically turns out slightly so the knee is pointing toward the interior of the car rather than straight forward. This outward position causes some rotation and tilt to the pelvis which affects the rest of the spine.

One of the best all-around positions for the back is the following: lie flat on the floor, with head on a very small pillow, head positioned so the chin is very slightly tucked toward chest. Knees are bent with feet flat on the floor. Arms are close to the body, palms facing UP. Relax and breathe deeply from the belly for up to five minutes at a time.

This position is a natural form of traction that allows the discs to unload and also allows the soft tissue around the spine to relax.

I make a point of doing this several times each day, especially after a stresful activity or if I have been on my feet for any period of time.

Check here for some good suggestions from the pros:
http://www.spine-health.com/wellness/exercise