Painful symptoms on the left side of the lower back and abdomen can be caused by the following reasons: 1. The most common disease that can trigger such symptoms is lumbar disc herniation. In patients with lumbar disc herniation, it is because the lumbar disc cartilage protrudes outside the vertebral body and compresses the lumbar nerve roots or even the spinal cord that triggers a series of uncomfortable symptoms such as lumbar pain, leg pain, and leg numbness. Because the lumbar nerves are widely distributed in both the lumbar region and the abdomen, once the lumbar nerve roots are compressed, there will be obvious pain symptoms in the lumbar abdomen. This pain will be aggravated by prolonged sitting, prolonged standing, prolonged bending, overexertion, etc. After lying down and resting, the lumbar and abdominal pain symptoms can be more obviously relieved. 2. Patients with kidney stones may also have pain symptoms on one side of the lumbar abdomen. Kidney stones may stimulate the kidney and ureter, triggering soreness or severe pain in the lumbar abdomen, and patients may not dare to change their position when in pain.