It sounds as though what you're describing is not a sore, which refers to a scabbed opening. having said that, i would add that as you must realize, there is no way to definitively diagnose what you have by reading a description or by scouring the internet. Your behavior was indeed not all that high-risk, but if you really want to know what you have so you can stop worrying, you need to stop examining yourself with such care and see a doctor. You will, I am confident, get good news.
Best.
Dr. Rockoff
The chance you contracted any STD from your encounter is zero. Given your description, it does not sound like herpes and even if it was its not likely you would have contracted it from this particular encounter. It's may be a sebaceous cyst, folliculitis, tinea cruris, maybe a number of other things but I highly doubt it is herpes. I believe that sores in relation to herpes generally start out as raised red bumps (water-type blisters) which could tingle, be sore, or itch and after about a day they become open sores for a few days. Then after they crust up and go away, generally lasting anywhere from 1-2 weeks. Your description does not match this in the least bit. I wouldnt worry about it too much. For reassurance have a dermatologist or your GP examine the bump to tell you what it is for sure. Herpes is not the likely diagnosis. Wait for the Derm in here to reply, but relax until then. You're fine.