Forget the focus on stretching, core and shit. Get your back checked out by a good athletic/sport orthopedic. I've been training seriously since 1976. I have had back issues since 1986. Did it stop me from the continual pounding? No! So, a year ago my ortho took an X-ray and saw that I had 3 disc completely gone. Went to a neuro-surgeon and had a mylogram done and he said I have DDD - Degenerative Disc Disease and I need a fusion surgery. A multilevel fusion surgery. All this caused by many squats, deads, bent over rows et al. I could go on, but I won't bore you. Surgery coming up, then the rehab. Can't wait to get back in the gym. This time a little smarter. Been thru a lot of different injuries and several other surgeries. Don't kill yourself in the gym. It will catch up with you.