There is a possibility of acute muscle spasm in lower back muscles. Does the pain also travel towards lower limbs as well.. There is a possibility of Prolapse Intervertebral Disc In lumbar region.
Next Steps
I would suggest you to take complete bed rest for now. Start with hot fomentation, analgesic, muscle relaxant, local analgesic ointment.
Health Tips
Avoid sitting down avoid heavy work, avoid Indian toilet, avoid bike riding.