Its probably a stress fracture. I had similar experiences. Many of them. Until I started wearing the right shoes and getting some pronation control stress fractures followed me around.
Anyways, that bump that you can feel is a calcium deposit where your body is trying to fix the cracking/cracked bone. If it hurts to be pushed on chances are its not something good. Your bones should not hurt if pushed on.
If you want proof that it is there just get a bone scan. It wont show up on x-ray until it is fully healed but will show up on a bone scan. They are a lot of fun to get (Ive had 2 or 3...cant remember). First they inject some radio active shit into you that has a pretty short halflife (so it gets out of your system relatively quick) then you get to go home and drink so water. A few hours later you go back and they put your shins under a scanner thing that detects the aforementioned radio active shit. If you have a stress fracture you can literally watch it form on the screen (more blood goes to that site and it shows the little hairline fracture).
Good luck though. Ive had a few that put a damper on running 2-3 years back during my junior and senior year. Sucked becasue I didnt get to train at all in summer and winter but oh well. Still was happy with the seasons. After a summer off they would go away but the bumps would still be there (no pain though).
Now go back and ask your dumb nonrunner doctor for a bone scan.