I had unprotected sex on ovulation day with withdrawal. took plan b after 12 hours. will plan b still work?

Plan B effect: Plan b is essentially taking a high dose of birth control to disrupt the hormonal patterns in your body to delay or present ovulation. An abnormal period afterwards is not surprising. If you think you might be pregnant check then check a home pregnancy test. They are cheap, reliable and available at any pharmacy. Always do a pregnancy test 10-14 days after to make sure it worked

Try Ulipristal/Ella: Unfortunately the primary mechanism of Plan B is the prevention of ovulation, but if the cat's already out of the bag, meaning you've already ovulated, then there might not be very much that Plan B can do. You may however call your doctor and ask for a script for Ulipristal or EllaOne which is more effective than Plan B and safe for the prevention of pregnancy at up to 120 hours. Good luck!