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If you did not have unprotected intercourse and always used condom then possibility of pregnancy is ruled out.Periods can be delayed by a day or so for various reasons as hormonal fluctuations,stress,any drug intake etc.Just because breasts are not sore does not indicate that you have conceived.
Wait at least for a week after the expected date and do not be stressed as it might delay the periods.If the periods do not start even after a week of expected date consider visiting your Healthcare Provider for evaluation.
Take Care!