Depends when you ovulate,this is only time you can concieve.if your cycles are short then its possible sperm can be waiting.if you have the average 28 day cycle then no.when we have periods and sex during them somtimes all the blood dont come away at once,spotting for couple days after even if we think finished can happen,just the after bits of period.
sperm can live a few days inside you so it is possible to get pregnant on the last day of your period,