Hi and welcome to the forum -
Do you mind me asking if you had unprotected sex at any other time in the month , (like approx 14 days ago?) If your period was due today, the unprotected sex yesterday would have not made any difference, as ovulation normally happens approx day 14 of a normal 28 day cycle. You are at your most fertile before during and just after ovulation.
You start counting the length of your cycle from the first day of your period to the day you AF arrives.
Hope that helps you XX