It sounds like it could be the beginnings of shin splints, but it's hard to say for sure. Here's an article you might find helpful: www.sparkpeople.com/resource/fitness_artic
Make sure you're wearing good shoes that fit properly and aren't worn out. Bad shoes can give you all kinds of aches and pains.
Hope that helps,
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford