I don't know if ankle-tendinitis is similar to foot-tendinitis, but I had the latter a couple years ago. In my case it manifested as this bizarre thing where I could walk for ~20min on a given day pain-free, and then all subsequent walking on that day was painful almost to the point of tears.

I found that although it was really hard to do (hello, student here!), staying off my feet was really helpful. I was back to normal within maybe 6 weeks of really not walking a lot. (It's threatened to come back a couple times since, but I've headed it off at the pass by not walking much for a couple days.)

I also suggest asking un_petit_mot. She reeeeally knows about this stuff.