If your menses are regular, there are least chances that you got pregnant with sex on day of expected menses .you might have conceived before that or you might have delayed period duee to some other cause.
please repeat urine pregnancy
test after a week &if it turns out to be negetive, take tab. Regestone 1 tab. twice a day for 3 days . you will get menses within 8-10 days of last tabs.