I had that exact pain also for a long time but despite orthotics, physical therapy and being very careful it just kept getting worse..I also had flat feet and was told i had posterior tendon dysfunction the year before...finally had an MRI which showed a torn posterior tibial tendon...after 3 docs and a lot of wasted time, I went to a podiatric surgeon and had flat foot reconstruction..it's a huge surgery as you will see on the posts here. Hopefully you have gotten to whatever is going on in your ankle early..do not wait because it will not get better on it's own..find a great doctor that can help you. Best of luck