see a health care provider? in the meantime, ice, elevate and don't put weight on it. Don't cycle on it if it hurts to do so. The ankle is one of those joints you don't want to screw up permanently.
Last year I had a grade 3 sprain (not cycling related). By staying off it and diligently icing for the first few days, I had a swift recovery and was back on my bike in just under two weeks. Admittedly I was careful (eg, not to touch down w that foot) until I was done with physical therapy.
Maryellen
2003 Trek 7500FX/standard saddle
2006 Trek Pilot 2.1/Serfas cutout saddle