Corsaire
Just for the hell of it and to rule it out, have a check up with a good sports oriented Chiropractor, you need to know how biomechanically balanced you are. For example: one leg could be a little longer than the other, even 1/8 or an 1/4 could make a difference...specially if you are doing heavy dead lifts, squats, etc, plus combining them with a highly stress activity like running.
Besides all that, you need to stretch a lot (not bouncing), hamstrings, lower back, glutes, back, overall. Plus, strengthen up your back and abs muscles. Proper form when lifting is critical, only after you got stronger on your abs and back muscles.
My left leg is slightly shorter than my right one, an d putting a thin padding on the left shoe heel made all the difference for me...my two cents.
Otherwise, by process of elimination and listening your body talk you might discover what's causing your lower back pain.....
Corsaire
Boarding party....AWAY!
"Security is mostly a superstition, it does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is not safer, in the long run, than outright exposure...Life is either a daring adventure or nothing"