What Causes Knee Discomfort, Ache With Pain On Walking?

I am not a runner, but my knees really start to feel funny and ache after I have been sitting crosslegged for a while, and sometimes they just start to hurt while im walking. They hurt in the front and feel kind of numb-like. I've heard of Patellofemoral pain (Runners Knee) , but Im not sure if I have it because I don't really run. Could i still get this "Runners Knee" if i'm not a runner? Do i have something else?