Lower back pain is a nebulous and common problem. Often, the cause of chronic pain can be traced back to a specific cause such as lumbar spinal stenosis, or degenerative disk disease.
But typically, lower back pain comes from something more difficult to diagnose, like overuse, strain, or stress.
It's also important to try to avoid back pain by staying active, and having proper ergonomics while sitting at your desk, if that's what you do all day. Keep your body relaxed and position your computer screen at eye level. A quick exercise or two can help stave off back pain. Source — Daily Rx