I used to have lower back pain usually after leg day and i figured out it was probably from inflexible hamstrings and bending my back forward when i squatted. i started stretching my legs and moved on to a new routine and it went away. now, i changed routines and a couple weeks later i have lower back pain again. im starting to think i have a weak lower back. i have good squat form. one difference in my new routine (purs) and my old one (ws4sb) is that im not doing any direct posterior chain work and im doing higher rep squats. what are some good exercises to strengthen my lower back/pc and how can i incorporate them into my routine. i had to skip my back work out this week because of the pain and have been taking 800mg of ibuprofen and it still bothers me.