If you are for sure ovulating and took plan b the same day after intercourse, what are the odds of the pill working? yes, it works by preventing ovulation, but what if you currently are and had sex, what's the best options to prevent pregnancy?

Plan B is for emergency contraception, and is not as effective as conventional contraceptive measures, such as condoms. BC pills, etc. The best option is abstinence, but most will not adhere to that. No contraceptive method is 100% effective. It is my understanding that plan B is 85% effective if taken withing 72 hours, more effective if taken sooner.

Because "Plan B" types of "emergency contraception" are not 100% effective, and depend on only partially effective prevention of implantation of the fertilized egg, unprotected sex during ovulation is more likely to be ineffective as the interval prior to implantation is short. Obtain a serum HCG test if your menstruation is delayed.