My guess is you do not have anything sexually transmitted at all--that the onset was merely coincidental with the sexual exposure you describe. The distribution of lesions indeed is most suggestive of folliculitis (hair follicle infection). Conceivably you have molluscum contagiosum, which can be sexually acquired, but that condition takes several weeks to show up, not 3 days.
So speak to your GP about the possibility of molluscum--and in any case, follow his or her advice about further evaluation or treatment. Aside from molluscum, you can be 100% you don't have an STD, or anything else that will ever harm your health or that of a future sex partner.
Final comment, in relation to "am I just being paranoid": When a person suggests that his or her own symptoms have a psychological origin, s/he probably is almost always right.
Good luck-- HHH, MD