Aside from all the really excellent observations and suggestions, I'd like to suggest a chiropractor for yourself. The way you describe the feeling in your ankles sounds like pinched nerve. IF that's the case then it probably isn't too bad right now but of course it will get much worse as time goes on.
I know not everyone is into the chiro thing and I can appreciate that. A lot of times chiropractors will offer reduced or even free xrays and or exams for a first time patient. You could just go for the consult and see if there is anything going on in your lower back which could be causing the problem. And likely it is being caused by the way your riding which is an easy fix. Yea!
Barring all that, try some pilates, stretching or yoga. That will go a long way toward easing the muscle tightness in your lower back which will release pressure on your spinal nerves.
Hope that helps a little.