I have had my fair share of broken bones, and I can say that none of them (except when my knuckle got crushed into itself) hurt nearly as much as a sprain.
When it breaks, you can kind of hear it. Did you hear anything really weird--not a "pop" really, but a "chhhk" sound?
Sprains really suck, and they never seem to go away all the way. I'd go to a doc right away and get a stablilizing walker thingy. Take care of yourself!!