hi, i have a similar problem since couple of months, infact currently i m on physio for my knees and hamstring...the docs diagnosed VMO weakness and ITB tightness due to which i have severe pain in my knees (outsides and in the centre) while i climb the staris or be in sitting posture for long and so on (my knees kinda get locked and cant be moved further down)...i can absolutely not do lunges and squats is also not possible with weights...!! i have been taking "jointac" a painkiller / Wikipedia reference-linkanti-inflammatory med for 3 weeks, not too sure if it has helped...but the stretching / electric treatment on knees indeed has.
My query is: the docs think it cud be due to lack of exercising, but i m active with my gymming and have been pretty much doing my regular lunges, squats, leg press etc with good amounts of pounds...!! the knee pain had surfaced bout 10 yrs back, but nothing was then found in x-ray...it has now suddenly cropped up and giving me trouble. Also when i do enough stretchings i m comparatively fine, but if i skip it for 2 days or so, it gives me trouble the next day...i do not wish to continue like this for sure...kindly suggest!!

Cheers!!
AK