As for the crappy shoes, sit vs. stand, excercise, posture stuff, the suggestions are appreciated, but when I say "pain" (as it relates to the lower back,) I'd file it under "excruciating/agonizing" when it goes out. During the worst recent one (couple years ago) I had to have my wife help me get into bed, and vividly remember screaming in pain. That kinda pain.
Back(har)story:
When I was maybe 10 or 11, I did what all the cool, bored, non-wealthy kids in my town were doing in summertime, and spent the day swimming in the local canal, jumping in from the 30 or so foot bridge. I hit the water ass-first at some point, and I'm guessing that's where this E36 M3 all started as my back was berkeleyed for days.
Never had any more trouble until I worked at a carwash for a couple years in college. I never realized how bad it was until I quit, and felt like a teenager (which I was) again, instead of an old man. The pain was constant, and it took me a long time and a "routine" just to get out of bed every morning.
When I was 23 or so, working for my last employer was when it got bad. I was helping our delivery dude
unload his truck, grabbed a box of glass, turned, and felt/heard that squelchy deal in my lower back, and hit the ground. I had to learn to clutch with my right foot as it was agonizing to do with the left.
I hated to do it, but I filed a claim under workers comp. They took an xray, and basically said "everything's fine. HTFU." and sent me to a physical therapist, whom I waited for for an hour only to have her basically hand me a couple pages of stretches/exercises, which I still do to this day.
As far as the original post, like I said, I was moving a bigass bass cab when I berkeleyed my upper back up. It sure as E36 M3 ain't from sittin around all day!