It because of lack of muscular strength of your back which generally occurs in case of overuse of muscles.
Next Steps
Go to a physiotherapist.. Ultrasonic therapy +IFT +Heating therapy +some strengthening as well as stretching exercises will be helpful for sure.
Health Tips
At home.. Rest +hot water fomentation +pain killer gel +no long sitting /standing /travelling/driving /walking /stair climbing /computer work +table work/no forward bending +no weight lifting +no manual exertions +sit tall.