Hi, I Usually Have A Regular 28 Day Menstrual Cycle.

Hi,
I usually have a regular 28 day menstrual cycle. After having unprotected sex on day 8 of my cycle, I took the morning after pill just under 12 hours after! My period is now 6 days late.. I'm feeling nauseous but somehow I feel like it's just panic/ imagination convincing myself that I am pregnant. Do I have cause for concern or would emergency contraception be the cause of such a delay?

Thanks for your time