What Causes Pain In Knees And Legs?

I have been having a problem with my legs. The top of my feet hurt, my knee is painful and I can only walk a few minutes before my legs give out. This started when walking about 20 years ago and has come and gone and now is here to stay looks like. I legs hurt from the knees down. My lifeline test shows good circulation. Could a blood pressure medication cause this? What kind of doctor whould I see?