No one knows whats wrong with my knees ?

my knees have been hurting since '04 and I have gotten x-rays and everything and they still dont know what is wrong. It started out with my right knee. It is always swollen and hurts frequently when I run or even walk and sometimes my left hurts when Im running. I can feel the "creaking" when I put my hands on them and move them (my knees) around. One doctor said its because I have flat feet but I dont believe thats the case because my mom has flat feet and her knees are fine. What could be wrong? no rude comments.