The fact that the pain radiates down your legs when you walk suggests that you have a problem with nerve compression in your lower back. Spinal stenosis (narrowing of the spinal canal as we age) or a herniated disc can cause this. If it doesn't go away in the next few weeks I would suggest going to a primary care physician for an evaluation. Both of these problems can often be treated very effectively with conservative care like physical therapy, and surgery is only needed in a fraction of the cases.
