What did you do during the sexual encounter? Did you perform oral sex? Unprotected sex? Vaginal? Anal?
Herpes could appear this early, but it's EARLY. The absolute minimum is 48 hours.
I'd be more inclined to say this is an allergic reaction to something you've eaten, or maybe you've somehow bitten the area.
It doesn't look like herpes, either. No other STD would give you mouth sores except syphilis, and syphilis symptoms don't appear for 10 days minimum.
It's hard to say if you had a risk for oral herpes without knowing if you even kissed.
If you get blisters there, get into a doctor ASAP to get it swabbed. Go to an urgent care if you have to.