Today I visited a new physio, who explained that he thinks my foot is sitting in the ankle socket in a strange way, meaning the cartilage is rubbing and becoming inflamed. So he waggled my foot for a bit then pulled it really hard!
Initially the joint felt a bit looser and ok, but right now it hurts and I'm icing it. I'm a little concerned about a setback, because I REALLY want to do the Triathlon on September 6th...