Hi Jo-
I know this can be a confusing time. The unfortunate thing is anytime you have unprotected sex there is a chance of pregnancy. Sperm can live up to 5 days, so it could have coincided with ovulation. The best thing you can do right now if you do not want to get pregnant is to not have unprotected sex and when you end up being 5 or more days late for your period, you can take a pregnancy test. There is really nothing else you can do right now but wait it out. Sorry to say. If you end up missing your period, you can go to http://www.optionline.org and they can help you with a free and confidential pregnancy test.
I hope this helps a little…sorry I can’t offer much more right now.
Luv- Molly