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If your fertility has returned back immediately after stopping with birth control pill use, then the ovulation would have occurred after your withdrawal bleeding which occurred after stopping with the birth control pill use. If your due date is August 5th, 2012 (completion of 40 weeks of gestation), then your probable ovulation would lie between November 9th - 17th, 2011 (calculation based on regular menstrual cycles of 28-30 days). The intercourse that was closer to your ovulation time will likely result in pregnancy. The chances of full ejaculate containing more number of healthy sperms are higher than in pre-cum/intercourse with use of condom. 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.