What Causes Dark Purple Blotches On Ankle?

Cool. I have had two squarish dark purple blotches appear on my right ankle, for over two months now, and they have not diminished in the least...they remain very dark. One blotch is on the front, and one is on the right. I know I haven't banged my angle against anything...but if I did, why would the dark blotch show up on two sides? Thanks for your help. I have no decent medical care, just MediCare...and I am limited only to going to emergency rooms.