It can be due to wrong posture assumption /disc bulge in the back/die to any fatigue or overuse of the back muscles/prolonged posture assumption (sitting /standing /travelling /driving for long).
Next Steps
Go to a physiotherapist..Ultrasonic therapy +IFT +Heating therapy +some strengthening exercises will be helpful.
Health Tips
At home.. Rest +hot water fomentation +pain killer gel +no long sitting +no forward bending +no weight lifting +avoid cold exposure +no manual exertions +no long sitting +no long travelling+no stair climbing.