Before any of us make sugggestions, you needto have a doctor diagnose exactly what is going on with your back.
In the mean time, read all the threads about core stabililty. You may not be able to do some of the exercises with a back problem, but the idea of activating your core can be very useful.
Try this: Take a deep breath in, and fill your belly up with air. On your exhalation, draw the navel to the spine, then pull the abdominals upward and inward, as if someone is giving you a Heimlich maneuver. Hold this contraction for 10 counts. Do this 10x a day, holding each contraction for 10 seconds. This will train your transverse abdominals, which support the lower back, to be more active.
Another point is one of technique. When you a "gradient" is your weight shifting backwards. This would put a good deal of pressure on the lumbar region.
But to reiterate, it is CRUCIAL that you get a doctor's diagnose!