Back pain, particularly in the lower (lumbar) area of the spine, is a common medical condition. Pain in the back can caused by many things, from injury to a muscle or ligament, to serious injuries to the spine, illnesses like fibromyalgia and kidney disease, the strain of pregnancy, and more. Most back pain goes away on its own in four to six weeks, but seek medical help if severe pain comes on suddenly, spreads down the legs and causes weakness and numbness, or is accompanied by fever.