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If you have been on birth control and have not missed your pills ever , then at the fag end of your cycle if you had unprotected intercourse where the endometrium is preparing to be shed, the chances of fertilisation and pregnancy are minimal or next to none. You should get your withdrawal bleed in the last 7 days of inert pills or after you finish the pack , which would further ensure no pregnancy.
I hope i have answered your query,
wishing you good health,
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