It could be arthritis, happens as we age. With age, intervertebral disks begin to wear away and shrink. In some cases, they may collapse completely and cause the facet joints in the vertebrae to rub against one another. This "wear and tear" on the facet joints is referred to as osteoarthritis. It can lead to further back problems, including spinal stenosis. Regular routine of back exercises can prevent low back pain and/or reduce the severity and duration of any "flare-ups." Controlled, gradual, progressive back pain exercises can help the back retain its strength and flexibility. Also, back movement promotes the delivery of nutrients to spine, keeping discs, muscles, ligaments, and joints healthier.
Please check these links: http://exercisesforinjuries.com/4-strengthening-exercises-to-relieve-back-pain/