Had Oral Sex. Spot Like Cigarette Burn On Leg. Turned Purple After Bandaging. What Do I Have?

Hello, first sorry about my english, I had an oral sex with someone with unknown hiv status. I recevied and performed, both with different condoms . one week later, suddenly in my right leg, there is one spot like a cigarrete burn but there is like a mus in it. since i am a smoker and thought perhaps just a ciggarete burn i used a bandage , just now (two days later) i open the bandage, and that one spot suddenly turned into purple with a big size. can u help eplain to me what i have? im really scared.