This pain is in lower back-it can be due to any wrong postural habit/disc bulge.
If its in tail bone(at the lowest point of your spine creating pain on sitting on hard surface) - it can be due to cooccydaemia. It should be assessed, diagnosed and treated by a competent physiotherapist.
Next Steps
Go to a physiotherapist.. Ultrasonic therapy +IFT +Heating therapy +exercises will be helpful.
Health Tips
At home.. Rest +hot water fomentation +pain killer gel
For lower back-no long sitting +no forward bending +no weight lifting +avoid cold exposure +no manual exertions +no long travelling +no stair climbing+use lumbo sacral belt(support) .
For tail bone pain -avoid sitting on hard surface+no long sitting +use cooccydaemia ring