Could be anything. Not to worry you, but maybe it's time to go to a doctor and get tested anyway. A lot of time herpes shows up as just a small blister or two. You can get it from oral sex also. And get in on the areas not covered by a condom. A lot of doctors don't recognize herpes unless the breakout is much worse. You will have to wait a few weeks and get a blood test for herpes. They won't give you the test unless you explicitly ask for it. Now, I am not expert in what different diseases look like, but it can't hurt to get your tests and results. If you are clean, then you can show the proof to your partners.