Hello there, You are absolutely right when you say that timing unprotected sex to occur just after your period is least likely to result in conception.
You have shed the lining of the womb and you are not due to ovulate for at least 9-10 days after the first day of your last period, so theoretically you have a window of opportunity to exploit.
You could also, in fact, enjoy unprotected sex during your period provide, you and your partner have no aesthetic objection to that.
But accidents do sometimes happen, either because periods may be. irregular or because of unforeseen hormonal fluctuations of which you are unaware.
Consult Gynecologist for further evaluation...