Help! All of you foot experts... Get me pointed in the right direction so I can determine what I'm dealing with here.

For the past several weeks my outer left ankle bone has been sore to the touch. Swelling directly behind the ankle bone, so I really don't have an ankle on that side anymore. Pretty much can't put on a pair of shoes because they press against that spot, so sandals are it. Ironically, my cycling shoes don't bother me. Yippee! The only time it hurts when I'm walking is going down stairs or up hills. (Go figure.)

Haven't injured it -- no trips, falls, errant kicks -- and my Achilles, calf muscles, etc., all seem fine. I do remember having the same issue last year, but not to this extent. Didn't do anything special, and it just resolved itself.

I ride 100-200 miles per week, and there haven't been any changes to my training schedule, the bike, or my shoes. I'm flummoxed. Any insight/suggestions will be greatly appreciated.