hello. I have been having pain in my knee. its not so bad, i have no trubble walking or running, just sometimes it cramps. It is not swallen or any color. i read about bone cancer starting in the knee and it says that pain would hurt alot when resting. when i rest i may get a cramp but it dose not last long and it dose not keep me from sleeping. should i worry. any advice? how dose some one know if they have cancer or somthing they should atend to a doctor?