Shin splints. The following may help:
-Better/new shoes
-Better warmups, specifically involving the shins
-Softer running surfaces - grass or sand
-Treadmills - different dynamic, may not be as tough on the shins, especially running on an incline.
If all of those don't help, you'll have to avoid or limit running. Fast walking's a decent alternative and doesn't cause the same pounding.