The pain in the lower back every morning may be caused by the following underlying diseases: 1. The most common disease that causes pain in the lower back every morning is lumbar muscle strain, which is characterized by increased pain in the lower back after a long period of bed rest and reduced pain after a short period of activity, but if the activity is prolonged, it will still lead to pain. 2. The reason for the pain is that the pain may be caused by ankylosing spondylitis, rheumatism, rheumatoid diseases, and tuberculosis of the spine, all of which can lead to back pain in the morning, some of which may be accompanied by morning stiffness. 3. The pain in the back every morning may also be caused by smaller urinary stones.