" I am wondering what other diseases there are that have severe lower back pain as a symptom. "
Have you ever heard of TMS? It stands for Tension Myosis Syndrome and describes how how muscle tension can cause chronic pain. Dr. John Sarno has written a few books on the subject. There are no exercises, you just learn to relax the muscle tension.
Elaine Petrone has a "Miracle Ball" program where all you have to do is lie on 1 or 2 soft, air filled rubber balls. Again, no exercises. You just (1) feel the pressure of the balls on your tight muscles, (2) breath, and (3) relax.
I would write more but the moderators won't allow it.
Good Luck