Posterior tibial dysfunction

Last October I ran my first traithalon (on the 1 year anniversary date of my open heart surgery). About halfway through the run I had almost unbarable pain on the lower-inside of my ankle. I was afraid if I stopped it would tighten and I wouldn't finish so I just delt with it. As soon as I crossed the finish line I sat down and that's when it got worse. Long story short......I have had problems with it ever since. I have a plate/screws on the ankle in question from a nasty break in 1995. So I went to the surgeon thinking it was the plate, but he told me two things...(One)- that it was posterial tibial tyndon disfunction, and (two)-no races (running) this spring. Since the second thing he told me is out of the question, I really need some advice. He told me that there are 4 stages of the degeneration of the tendon and that I am in stage 1.

Also, if I have to....What is the shame level regarding walking/running during the run phase of the race.

Thank you