Thanks for the query.
It is quite unlikely that the rash could be an STD related rash as the exposure is a single one.
However, no genital rash after an intercourse which persists or appears must be considered for evaluation. Many of the organisms have an incubation period around 3 to weeks and hence present with early symptoms of rash, joint aches,etc.
Kindly consult a dermatologist personally for an examination and further management.
Hope this helps
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