Hard to diagnose from here. All I can do is make some suggestions, hoping one of them rings a bell.
A swelling in the ankle without an obvious cause like an injury or recent stress on the ankle (like what happens to beginning runners) is mostly caused by circulation problems. As already advised, light walking might help, because the regular contractions of the leg muscles help pump away the excess fluid.
Changes in medication could also cause these symptoms. Both starting some med and quitting some med may cause local swelling.
Another cause might be a fluid imbalance. Does your face seem more “puffed” than, say, one or two years ago?
Fluid imbalance could in turn be caused by electrolyte imbalance. Did you recently change your diet such that your salt intake is now significantly different than before? Are there any other changes in your diet?
The final thought that comes to mind is one of the forms of diabetes. Have you recently experienced forms of dizziness, extreme tiredness, craving for food, excessive thirst, or urine changes? If you tap your toes lightly with a paperclip or so, are your toes about as sensitive to the touch as your fingers?