I have tweaked my lower back on a few occasions, when pushing squats too far or too fatigued, and my form breaks, causing me to lean forward. It's probably not nearly as bad as the problems others in this thread are having, but for minor pain, this advice may help.
The 90/90 breathing exercise does WONDERS for it. It's actually quite amazing how you feel things "fall back into place" when doing your first few reps.
Might need to watch a couple videos to fully understand it. I'm not sure which ones are the best.