I have recently begun jogging to get in shape. I never really did any physical activity before, but running feels pretty good. The only problem, though, is that maybe 15 minutes after I finish my run, my knees start to hurt and minor swelling occurs. What could this be? After a few hours, everything goes back to normal, but this must mean something? I have been running once per day for about 2 weeks, and it has been the same thing every time.