A week ago I had sexual contact with another man I do not know. We kissed, engaged in oral sex (unprotected but before ejaculation) and he rimmed me. We ended with masturbation.
Now I have developed what appears to be a blister on my right buttock along with reddish inflammation around it. Further down from that I also have a few (2-3) zits. I'm scared I have herpes, gonorrhea, syphilis, or any combination of STDs.
What could this be a symptom of?