Hi,
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If the intercourse was closer to your expected period dates, then the orgasm resulting in uterine contractions leading to bleeding cannot be ruled out (precipitation of early periods). If the bleeding is light and stops within 24-48 hours, it could also be suggestive of possibility of cervical problems or presence of uterine fibroids, polyps, ovarian cysts etc. Visit your doctor/gynecologist for further examination and investigations to look for the underlying cause for the bleeding. Wait and watch for your next expected periods.
Take care.