You need proper assessment, diagnosis and treatment. It can be due to any injury/problem in the back or due to leg muscles tightness. Consult a physiotherapist.
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 walking /standing /travelling.. No cold exposure.