My mom is in training for a marathon, and had to quit after complaining of severe pain in her hips. She went to the doctor and after bone scans, x-rays, and the like; the doctor said it was burrcitous (I'm sure I'm spelling that wrong). At first she thought it was arthritis, but it just kept getting worse. She's not allowed to run anymore.
I would go to a chiropractor for this problem. You may be out of allignemnt.
Do you have any instep problems?? My foot rolls out when I walk and this was giving me problems in my knee when I walked. I went to a 'propper' athletics shoe store and actually spoke to someone who knew the ins and outs of all the shoes. They fited me with a pair of joggers that counteracted my rolling out and I immediatly noticed the difference in my knee while walking.