Does the pain travel under and behind the medial malleolus ( bump on inside of ankle )? If so, that is a very common site for posterior tibialis tendinitis. Most likely a foot mechanics issue, or foot placement issue. You can't "run through" most tendinitis', they will eventually make you shut down. i am assuming your season is here, so i wouldn't mess around and self-treat. I would see your Sports Med doctor, ATC, PT etc.