Leg Pain

I'm not entirely sure if I hurt myself somehow or what is going on but I am experiencing a menacing pain in my left leg.  It goes from my shin through the knee and up into the thigh.  I don't quite know what I would have done.  Nothing to severe where I heard a snap or a crack.  It simply just began hurting.  Hopefully I can get it under control and figure out what the cause is.  I am hoping some stretching can ease the pain a skosh.