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Taking an Emergency Pill could explain the sudden bleeding after 2-3 days. It could also be due to other causes in the genital tract. Nothing to worry. Wait till your next period, though it may be delayed by a few days and may have heavy bleeding as well. I would like to advise that putting in the penis and not ejaculating could also cause BOTH Pregnancy
and STIs because when a man is sexually excited there is formation of pre-ejaculate
which is rich in sperm as well and through this route STIs can also spread. Next time use a barrier contraceptive
like condom in such cases.