It can be due to many reasons.. If you walk in pain, it increases with time. Driving+long sitting + stair climbing increases this type of pain.
Next Steps
Consult 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 standing /walking /stair climbing +use knee cap+avoid forceful knee bending+no cold exposure