who is the father of my Baby Guy A or Guy B?

Hi,
Welcome to ehealthforum,
Early ultrasound scans can detect gestational age with accuracy of +/- 5-7 days. The bleeding after taking emergency contraceptive could be the withdrawal bleeding (usually occurs within 5-7 days of taking the pill indicating that it was effective). If there was period between two different sexual encounters, then the intercourse after periods would result in pregnancy. Taking your LMP as Oct 1st (the withdrawal bleeding date as described by you), your next ovulation would be around Oct 15th, and conception could have occurred between Oct 11-19, 2011, and your due date would be around July 7th (completion of 40 weeks of gestation). The ovulation usually occurs 8-14 days after your first day of menstrual bleeding (the exact date of ovulation can vary from woman to woman) and the intercourse closer to ovulation time results in pregnancy, and so the actual conception date would correspond to date closer to ovulation date. Ultrasound scans done for dating can also help with knowing your probable conception date. The exact results can only be made out after a Paternity test. Visit your doctor/gynecologist for further assistance and clarification.
Take care.