Knee Pain[MEDICAL MYSTERY. X-ray scan]

Hi Doc, [THIS CASE IS A MEDICAL MYSTERY,NO ORTHO YET HAS UNDERSTOOD] I am experiencing mild to semi-severe knee pain(left knee) since an year. The Pain usually emerges when I'm in home or in holidays(when I don't do much walking or running) On the other side, I won't experience any pain during weekdays when I; walk , run , do exercises etc.. as usual. What may be the cause for it(I'm jus 20 years old) I don't have any previously recorded trauma, I have even consulted many orthos only to find that nothing has happened. BUT STILL THE PROBLEM PERSISTS.. For the record from the day my problem started, almost an year ago I experienced severe pain in my left knee for about a week, without having met any trauma. [NO IRREGULARITIES FOUND IN X-RAY SCAN]