Hello and thank you for the question.
Answers given are for informational purposes only and are not meant to replace an exam by an in-person.
I am Dr. Sohaib, a practicing Internal Medicine Specialist and i will do my best to help you today.
Most likely this is a result of localized irritation and inflammation which settles down spontaneously; because STD's like herpes or other do not appear so rapidly after the sexual exposure.
However, we still can not rule out the possibility of an STD (as there is a possibility that you might have an infection already which did not appear or become symptomatic until now).
So if there is any itching in the affected area, take benadryl.
And see your doctor for a clinical examination and STD screen, which will put your mind at ease also.
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