I have a rash under my arm, which started today, which is burning and paining while moving my shoulders. I have attached the pictures. I tried to poke it with a needle to see if it is a blister and any liquids come, but only blood came out of it. I am worried that it will be related to HIV since I had exposure eight days ago. The exposure was mutual masturbation. I also think that it is the rash, which is related to heat. I was wearing a sweater, and maybe it is caused by heat or sweat due to too much friction. I have a history of Von Willebrand disease type 3. And I currently take Sertraline. Please advise.