Your complains are suggestive of a patella issue. chondromalacia patella is a common condition which is aggravated on climbing stairs, sitting cross legged or any activity involving the squatting action. So avoid such activities for a while. Take a lift where possible, avoid sitting in the floor or using an India commode toilet.
X-rays are normal in chondromalacia patella unless grossly neglected leading to bone changes.
Next Steps
1. pain killers in SOS basis
2. Open chain Knee strengthening exercises available on Google. any exercise which does not involved aggressive squatting action. gentle half squats can be done.
3. use ankle weights available in different weights, start off with the least
4. apply cold fomentation immediately after physio for 5-10 mins.
5. if the pain does not subside in a month,
MR Cartogram needs to be done. this is the investigation of Choice for Chondromalacia Patella
6. all this being said, the problem could be due to a meniscal injury or some injury which cannot be picked on an x-ray. please visit an orthopaedic surgeon if the pain persists beyond 3 weeks