It sounds like you have an issue with your patellar tendon where it inserts on your shin bone. I had a bad case of patellar tendonitis last year and that was one of the places that it hurt.

I hate to say it, but the 40 min run was probably too much to start with. Not that you need to hear that now.

So, if it is an itis, rest, ICE, ICE, ICE and I would probably start thinking about some strengthening exercises. Can you get a script for a few PT sessions?

If not, if you google, you can get the exercises.

Good luck.