If the sex was unprotected then it is possible that one could be pregnant, so to be sure please take a home pregnancy test after 10 days of unprotected test. Also if you have taken emergency pill then it is a possiblity that it could have affect the period cycle, please be relaxed and do not take anymore medicines without consulting a doctor. The reason of pain could be tension or pressure, please be relaxes and you could also consult a doctor to know the exact reason.
Please read:
https://lovematters.in/en/resource/unplanned-pregnancy
https://www.fpaindia.org/
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If the sex was unprotected