I am a 36 year old male whom plays soccer and flag football on a weekly basis, over the last few months I noticed after running about 30 minutes into a soccer match I felt some sharp pain and weakness in my left leg, i noticed that there is a bone sticking out on the left side of my knee on my left leg, the pain usually last for a few days, then the bone seems to go back into its normal position, i dont have that problem on the right knee. What could that be and what should i do?