you might be getting shin splints or your not getting enough vitamins to sustain your muscles
it sounds like shin splints, i had those for a while
my solution was new running shoes
you see, for shin splints, you're not getting enough support in your feet, so the tendon becomes inflamed which causes the muscle to take the pressure sustained from running when you hit the gound and transfers it by tightening around your shinbone
get better shoes (in turn, support so that does not happen)
good luck