emergency contraception
"Had unprotected sex the day I was ovulating.  Within 12 hours I took Plan B.  Five days later I had a bad backache and woke up with cramping and what I guess was heavy spotting that lasted about 3 days.  My period was due on a Tuesday but started that Saturday (5 days late).   The only real side effect besides the spotting was I was very irritable the week leading up to my period and I never ever have PMS.  I would recommend this highly if you get yourself into a similar situation.  Of course condoms, BCP, IUD etc… are a much better option."