I had sex with guy a on night of 8/9 and he ejaculated inside, no condom. guy b was on night of 8/11 and he withdrew, no condom. i took a plan b on morning of 8/12 about 12 hours after guy b. i am pregnant, who is more likely to be the father?

Guy A more likely: This situation is a good argument for saving sex for a committed marriage relationship. Plan B is designed to prevent ovulation & is usually effective when taken up to 72 hours after intercourse: thus if taken at the time you said, would not likely prevent pregnancy from Guy A (too late) but would prevent from Guy B. If you had a conception from Guy A the plan B would possibly not affect it.