without a proper exam and history I can't be sure, but here are a few of the simple ideas....Leg pain with running can often be corrected with a good shoe fit! make sure that if you are pronator, you are wearing a shoe for someone that pronates and have your friends that is a PT watch you run on a treadmill. He or she might be able to see if you have muscular imbalance causing you gait to be altered! A tight muscle here and a weak muscle then can cause flawed gait and pain. But it be sure I would have to know a lot more!