There are a lot of reasons responsible for back pain. It can be due to posture, any disc bulge, spondylosis, spondylolisthesis or any other cause. Or if its at the end of the tail bone, it can be due to cooccydaemia.
Next Steps
Consult a physiotherapist.. Ultrasonic therapy +IFT +Heating therapy +exercises will be helpful.
Health Tips
At home.. Rest+hot water fomentation +pain killer gel +no long sitting, no travelling, no cold exposure, n9 weight lifting , no sitting on hard surface, no forward bending, no exertions, no stair climbing. .