Knee pain since childhood

Ever since I was in kindergarten my knee will hurt fee times a week, it used to be so painful that I would hug my leg while crying, it hurts on one side then the next after awhile. Sometimes both at the same time. I do not remember any incident of a bad fall which can injure my knee to that extent, never have i had the experience of a fracture. The pain feels like the pain of a knee cap? It hurts randomly, regardless of the weather or what I do. However, during times where I exercised intensely it will hurt to the point where I have difficulty walking even when I was 16, very capable of tolerating the pain after growing up with it for a few years. I stopped growing at 12, so growing pain is unlikely. I’m 22 now and still experiencing the same pain regularly.