Pain on the bottom of my foot...

I've been training for the Santa Barbara, CA tri (1mile swim; 34 mile bike; 10 mile run) for the past couple of months. Last week, about 8 days ago, I started having a great deal of pain on my the bottom of my left foot, shortly after a run.

The pain starts about a 1/4" from my left heel (going toward my toes), is just on the left hand side of the bone on the far left side of my foot. The pain then radiates up into the lower portion of my fibula.

The pain is generally not present before my run, and surprisingly doesn't start to appear until just after my run. Then, it is extremely painful, and very difficult to walk on. The pain lasts for about 12 or so hours.

I am 13 days away from my tri. What could be causing this pain and/or how do I alleviate this pain to ensure I am able to participate in the triathlon on August 23?

Thanks for your help!