If it turns out that it is plantar fascitis or something involving the tendons in the ankle, I would make sure to get into a physical therapist. I let something similar to what you are describing heal itself for over 10 months by resting and using anti-inflamitories - I started to feel better and began exercising again only to have it return in full force. Square one. I went to a physical therapist about three weeks later who manipulated several of the tendons in my arch, ankle, and toes. He broke up scar tissue and taught me some very strange, but effective stretches. I felt relief that evening. I went back a few times after that and was SO PLEASED with the results. Now if anything in my feet start causing problems, I get right in.
I also second getting custom insoles, although I used some that I purchased at a web site called Sole Custom Footbeds. I trimmed them to fit my cycling shoes, put them in the oven for a few minutes, took them out, slipped them in my cycling shoes, and stood on them for a few minutes while they made a custom mold to my foot. I love them.
Just my $.02
Let us know what happens!