Having worked with marines a lot break down with calf and lower leg problems. Most of the time its poor muscle control and conditioning.

As the other's have said get checked out by doc or physio, but if your regularly running 10 miles or trying to possibly with a wieght on then you need to be stretching regularly and conditioning your legs with some strength type work as well. Though have it assessed by someone first before starting new exercises.

Also do you do any other type of training to rest your body from running eg swimming or cycling