My leg feels like circulation is being cut off?

[RainyDayGirl]

For the record I am 15 going 16 in a month. I just know some people ask for age. And a girl. So, anyway. Lower below my knee (on the back side) A few inches lower from it it starts hurting like circulation is being cut off. I walked around, stretched, nothing has worked. And just the other night my right leg was doing the same thing. If I moved really fast the pain would ease for a few seconds. What's going on? I'll use going to a doctor as a last resort. I want people oppinions first~