Pain might be due to acute lower back muscle spasm with a possibility of nerve root inflammation and prolapse Intervertebral disc..
Next Steps
You can start with hot fomentation, take analgesic with muscle relaxant, apply analgesic ointment locally.. Take complete bed rest for now.. If not relieved, you may require MRI of lumbosacral spine..
Health Tips
Avoid heavy work, avoid sitting down, avoid Indian toilet, avoid stair climbing..