Is your lower back tight especially on one side, more so than another? If so, your quadratus lumborum might be tight. You can stretch it by what I think is the worlds best lower back stretch. Simply put one hand on the wall and cross your legs. Dip your hips straight into the wall till you feel a little stretch and then push your butt straight back until you feel a big stretch. Hold for about 15 to 20 seconds, relax and repeat another 3 times. Make sure to repeat this on the other side.