Hello,
It looks like your problem became a chronic because you are having Pain, swelling, difficulty in climbing down stairs for 2 months.
Next Steps
I would suggest you to consult a physiotherapist and take a X Ray for your knee joint especially patellofemoral joint to rule out the cartilage damage.
Health Tips
Gradual but progressive quadriceps and hamstrings strengthening exercises to fix tour pain.
If your approach to your pain is just a medication and not heading towards a detailed examination and exercise rehabilitation, there is a chance to develop degenerative knee disorder.