How Can Inner Ankle And Foot Swelling With Bruising Be Treated?

my left inner ankle is swollen, and the swelling is the size of a flattened grapefruit surrounding my ankle. the area is a bit dark, right above the ankle (might be a bruise). it gets worse with prolonged walking or standing. i feel swelling in the sole of my foot as well. i am 21 years old and active (triathlete) but have never had problems with my ankles and can not remember falling or anything that would make it a sprain. what is it?