A Circular Open Dip That. Was Bleeding Seemed To Appear

A circular open dip that. Was bleeding seemed to appear out of nowhere on my forearm today. I had an itch there, and when I looked, that is what I discovered. I dabbed it several times, but continued to bleed , cannot remember injuring it in any way, now several hours later the skin surrounding the dip is darkened, cleaned it with alcohol and applied anti biotic cream