There are various reasons for acute back pain. Most commonly, it is due to acute muscle spasm in lower back muscles.
Does the pain travel towards the lower limbs.. Is there any difficulty in walking because of pain.
Next Steps
I will suggest to take complete bed rest for now, take analgesic with muscle relaxant tablet twice daily, start hot fomentation, apply analgesic gel over the site of pain for 3-4 times a day. If the pain doesnt get relieved after medicines, you may go for one X ray of Lumbar spine
Health Tips
Avoid heavy work, avoid sitting down, avoid Indian toilet, avoid forward bending..