Ive had knee pains for a long time, pretty much since i was around 12. It does not constantly hurt. Some days its fine, others not. It doesn't hurt when i work out, but rather when im running or jumping and putting my weight on that knee. But the other day i was running and it was fine, now today it feels like im getting stabbed with a knife. Its always like this. The pain is right below my knee cap. Any ideas?