I wanted to add that "Plan B" (
levonorgestrel) Emergency Contraception is easily available through most US pharmacies. You do NOT need a prescription of any kind! Simply ask the pharmacist for it, and they hand it to you. They don't even keep a record of your name, so your privacy is assured.
In my area, pharmacies are open 7 days a week, so you can get it first thing the next morning without necessarily needing to keep it on hand.
This drug is 2 pills to be taken 12 hours apart, as soon as possible after the incident and no more than 3 days after the "oops" occurred. It does not do anything if you are already pregnant.
Cost: about $50 in my area.
Plan B® One-Step: Home