Pain in my foot arches... what gives? (Read 409 times)

When I was travelling I ran on a hotel tread mill for the first time, Level 1 incline, and I hurt my foot somehow. The pain is sharp, like a sprain or muscle pull, on the inner arch of my right foot. I thought it would go away, but it's been a week and after every run I have this pain again. I walk with a sort of limp now. What's causing this? Does it have to do with pronation? Could it be just temporary or maybe a technique issue? My first instinct was to blame the treadmill but if it were a one-time injury, it would have healed by now, right? How do I prevent it from getting worse? Etc.