I have seen lot of patients with such complains and it is called chondromalacia patallae. It is softening of cartilage of knee cap, it can happen without any obvious cause, and may be triggered by knee exercises or running. I have following suggestions for you. first get MRI of the knee to confirm the diagnosis, and if it shows same conditon then : 1. Static quadriceps exercises. 2. Tablet Brufen for pain relief 3. Tablet Dicerin daily. 4. Avoid stairs and cross leg sitting, and running.