With no known injury to the area, the first thing to come to mind is a nerve problem, such as a herniated disk, spinal stenosis, or other spinal problems. However, it is important to assess lifestyle before jumping to conclusions.
If a desk job/a lot of sitting around/driving is normal for you, you may be putting the area through too much strain, and look into ergonomic seating options. Otherwise, i would see a doctor to discuss possible spinal problems.