Running with posterior tibial tendonitis

Hi! Has anyone experienced issues with posterior tibial tendonitis before? This developed for me 3 weeks ago and I have a run in another 2 weeks but I haven't done a decent long run since it happened. More specifically, after my first 10+ mile run it flared up and with icing and anti-inflammatories, I haven't done more than 4 miles since, and I have a half marathon in 2 weeks - and then first sprint tri of the season 4 weeks after.

I visited the ortho who said to only do as much as I can handle - but how do I know what that means? I tend to push too hard (don't we all??) and want to run the half but want to do any long term damage. Am I stupid for running the half marathon if I haven't done decent training for the month prior?

Help!!