Okay. The day your period starts is day one. If your cycle usually lasts for about 28 days, then you are most fertile around day 14. Sperm can live in the female body for up to 7 days, though, so any sex around day 6/7 could potentially leave sperm in you for your most fertile period. This means you are at risk.
The morning after pill, also called emergency contraception, is designed for situations like this. You need to take it within three days, though it's most effective in the first 24 hours. If you are beyond that time frame, then you will simply need to wait and see if your period arrive the following month - remembering that stress can influence your period.
If your normally regular period is around a week late, then you will want to buy a pregnancy test. Make sure to read the back of the box - some are effective as soon as the first day of your missed period, while others take up to two weeks to register pregnancy.
Pregnant or not, you'll want to find out as soon as possible so you can make the appropriate decision for you. Abortion is safer and easier earlier in a pregnancy, and if you choose to keep a possible baby you'll want medical attention as quickly as possible.
All of this is speculation, though. Chances are that you are fine. Many people try for months and years to get pregnant and it doesn't happen for them. Relax, breathe, and wait for your period.