Hi, i would rule out herpes because it usually take a week or 2 for blisters to appear so it may be a friction irritation from the act itself. Not sure why a second one appeared but it could be from touching the first one causing more irritation. You can have it swabbed now to see what it is.
It could be herpes, since it can appear 2 days to months later, which can be treated. Chances are you don't have hiv. It usually manifests as sweats, fatigue, sore throat, muscle aches etc when you are infected. Also, just simple odds are in your favor. Good luck to you.:)