Do you know what cycle day you were on when you had intercourse and which day you ovulated? Remember, sperm can only live in an ideal environment (meaning assuming that cervical fluid was favorable) no more than 5 days (and probably closer to 3-4 for most), so if your "accident" was more than 5 days before you suspect you ovulated, you don't have much to worry about. Also, remember that, even under the most favorable conditions (timing, physical conditions, etc.), we have much less than a 50% chance of conceiving each month, so try not to worry.
The pain you describe sounds more like ovulatory pain than early PG symptoms. Pregnancy symptoms don't being to appear until after implantation has occurred (generally 5-10 days after ovulation) and it's the production of the hCG hormone (which only occurs AFTER implantation) that causes symptoms. Some women begin feeling mild symptoms (nausea, fatique, food aversion, etc.) immediately after implantation, some not until weeks later. Ovulatory symptoms can very closely mimic pre-menstrual symptoms (mild cramping, breast swelling, etc.) for some.
Unfortunately, there's not much you can do at this point but wait it out. If your period is late, and you're sure you ovulated on time this month (i.e. not late...late periods are actually a result of late ovulation), take a pregnancy test for some peace of mind. Until then, try to relax and not worry too much!
Hope that helps!