The most common cause for back pain is muscle strain. If you have ruled out sciatica, you may also be experiencing unequal leg lengths or an uneven pelvis. During either condition, the muscles on one side of the body are being pulled long while the muscles of the other side of the body are shortened. Relatively weak abdominal and lower back muscles may also contribute to the problem. Pain in the lower back on one side, experienced in the lower buttock or along one leg can be associated with a pinched sciatic nerve. In most cases of lower back pain people benefit from exercises that strengthen the back and abdominal muscles. You may consult an orthopedist for further help and to diagnose the persistent pain in your lower back and leg.