If there hasn’t been used condom, you can’t be sure. About traumas that have been got during the sex (bruises, tears. etc.) you usually feel symptoms right away, but STD has incubation period. So symptoms of STD show up later, whether it’s next day or 3 months after intercourse. It would be the best if in such a situation person contacted a specialist because all the STD’s are best treated in beginning stage.