It can be due to any ligamentous injury /meniscal injury.
Next Steps
Go to a physiotherapist.. Proper assessment, diagnosis and treatment is required.
Ultrasonic therapy +IFT +wax therapy +some strengthening exercises will be helpful for sure.
Health Tips
At home.. Rest +hot water fomentation +pain killer gel +no long standing /walking +no stair climbing +no cold exposure +use knee cap.