Brother, take this seriously. Your lower back should never hurt after a workout (other than DOMS of course). If you're having strain-pain you need to find out the cause and quit it. Common causes of course are using too much back in squats, arching back too much on bench, or lifting too heavy on deadlifts/using too much back. Some people simply cannot do certain exercises, such as back squats because of their unique build--they do front squats, hacks, or leg press. Finding the culprit is the first step. Then, do the back stretches recommended by Drs. You know, the ones where you lay flat with palms on floor and bring a leg over to one side bent and hold it, and breeeath out. ahh. Back injuries are not joke. I've had (have) one. Don't be a fool like I was and push through the pain. It put me out of squating for almost a year and my squat has never been the same. I lost some quad mass too.