It can be due to overuse of back muscles or wrong posture assumption for a long time as in case of using computer system /travelling /long sitting /studies.
Next Steps
Go to a physiotherapist.. Ultrasonic therapy +IFT +Heating therapy +some strengthening exercises will be helpful for sure.
Health Tips
At home.. Rest +hot water fomentation +pain killer gel +no long sitting /standing /travelling /driving /walking + no stair climbing +no cold exposure +no manual exertions +no weight lifting +forward bending +correct posture (sit tall).