I have an unusual, recurring pimple-like growth on my knee cap. I first got one a few years ago, but it went away. Immediately after it left, another one appeared near the original place. Yesterday, it became large, red, and sensitive. It seems to be affecting a tendon or muscle in my lower thigh, for any quick bending of the knee, such as climbing and descending stairs and bending down, causes pain in that area. What is this and should I go to the doctor? From research, it might be a disease, or something to do with fluids from tendons or stress. Any help would be greatly appreciated!