Sounds more like a foliculitis.
It wouldn't be a wart from this encounter - the incubation period (time from infection to symptoms) is usually months long, though it could be from a previous encounter.
I agree that it doesn't sound like herpes.
It could also be molluscum, though again, the incubation period would suggest a different source.
It could also be something not related to sex- a fordyce spot, a hair follicle (though that doesn't sound likely, given your response), irritation, etc.
As you know, the only way to know is to get it checked.
There are low cost clinics all over. If you are in the US, google your city and state, and STD Clinic, or call your local health department (google your county and health department) for locations. Planned Parenthood also offers a sliding fee scale, so you pay what you can afford.
Doesn't sound like an STI due to the relatively small window between the event and the appearance of the spot. The incubation period for an STI which produces bumps/chancres/blisters is about a month, so this is too early.
There is more probability that it could be folliculitis ( infected hair follicle) or a bite. If there is a whitehead on the spot then that is probably the case.
Do you have any other similar spots in a line or cluster? If you then I would be looking at more towards a mite/insect..
If it is folliculitis, an antimicrobial soap and steroid cream can clear it up rapidly.. If it is a bite, then an insect bite cream will kill any itch