I started running a lot lately, 4 miles on the elliptical, 3 miles on the track right after. When I just did the elliptical, my knees were fine. But now my knees hurt when I run (No pain while I'm walking). I'm 22 years old, never before had knee pain or problems, and I use good Nike running shoes. Do you guys think I should take a few days off hoping it will go away or should I go see a doctor?