Most causes of back pain don't require immediate medical attention, but you should see a doctor right away if your pain is accompanied by any of these "red flags":
• Weakness or pain in your legs, especially if it goes all the way down to your feet.
• Loss of bladder or bowel control.
• Fever or tenderness.
The first two could be a sign of neurological damage, caused by compression of the nerve roots at the lower end of the spinal cord. A fever or tenderness may signal an infection.
Also, if you have a history of cancer, back pain may be a sign that it has metastasized.