About a month ago I had a sexual encounter. The condom broke but we stopped immediately, and I don't think I came in contact with any semen. A couple days ago I noticed a red bump, approximately 1 cm diameter on my pubic region, about an inch above where my vagina begins and on the left side. Today I noticed that a small red scab like mark has appeared in the center of the bump. It sort of looks like a popped pimple that's scabbed over, but slightly bigger. I haven't been watching it closely, so I'm not sure if it formed slowly or suddenly appeared. The scab is small, maybe 1/4 of a centimeter. I have absolutely no pain and I have no other symptoms. Am I being paranoid or could this be an STI?