What Causes Quarter Size Rash On Side Of Calf?

I have a quarter size rash looking thing on the side of my calf on my leg and it looks like a hickey/welt and itches occasionally, at first i thought it was ring worm.. but it never formed a ring, i've had ring worm before so i know what it looks and feels like! So its not ring worm, but idk what it is.. do you maybe have an answer on what it is and how to cure it?!