What you suffer is acute low back pain - most often caused by a sudden injury to the muscles and ligaments supporting the back. The pain may be caused by muscle spasms or a strain or tear in the muscles and ligaments. When you tried to bend suddenly may have caused this.
Next Steps
Most back pain gradually improves with home treatment and self-care, usually within a few weeks. Contact your doctor if your back pain: Persists past a few weeks Is severe and doesn't improve with rest Spreads down one or both legs, especially if the pain extends below the knee Causes weakness, numbness or tingling in one or both legs