Knee pain while walking, running etc.

Hi, myself Vishal. Once while squatting, i felt a severe pain in my knee. This was some 2 yrs back, it used to pain exactly when i was at 90 degree position during the squat. It also pains me if i tried to straighten my leg. I immediately stopped squatting and in turn did lighter weights for legs. I did not visit the doc for about 7 months, the pain persisted so i visited a doc and he suggested me to stop doing leg workouts and prescribed medications. He also saw my reports MRI of the knee and the x ray but said its nothing major. He suggested a few simple leg workouts which i started following. After 6 months of treatment, i did feel better now the pain was lesser and it stopped paining me while squatting. I have started doing bodyweight squats but it does pain when i try to straighten my leg. It also pains sometimes while walking, twisting. It pains if i stand for a long time or walk a lot. I still cant run. Plz advise!