i have lower back issues as well from time to time, like now, usually due to not warming up properly and huge swings out after cutting loose that over bend my spine. also from imbalances with my abs.
in these cases i usually start again doing loads of crunches for the abs, and also stretching, in two forms, one passive one and one active one:
- lie on the ground and put your feet on something high enough and close enough to your hips that your knees are 90° bended. your thighs shoul also point vertically, so that you form another 90° angle with your torso. lie relaxed for a few minutes.
- sit on the ground, with your feet to a wall so that they are vertical; place your hands behind your head, then start rolling over onto yourself towards your knees. you start attaching your chin to your chest, then you keep going down as much as you can. if you go more towards your knees you'll stretch also the back of your thighs, if you go more towards your pelvis you stretch more your lower back.
hope this helps, it's what i'm going to be doing in a few hours.