First of all, unprotected sex just after period over is quite safe and taking unwanted 72 within first 24 hrs gives additional protection against unwanted pregnancy
. Here, chance of being pregnant is almost nil literally.
A withdrawal bleeding usually occurs within 7-10 days of taking the pill and next cycle may be delayed or earlier (7 days) due to hormonal
imbalance and mental stress
Wait for next coming period and don't be much worried. Practice safe sex