I am 34 year old male. I got hurt on my left knee in 2015 and the pain took quite some time to go. But now after longs hours of sitting, if I start to walk, it pains and the movement is not smooth (doesn't happen after a sleep, it happens mainly when I am working on my laptop or sitting in a car for a long time). It takes some time to come back to normal. Please let me know WHY this is happening, if this is serious or it will heal naturally with time. Are there any exercises etc that can be done to bring it back to normal.