I am confused about when I conceived and what the due date of my baby is. My last period was May 25th, 2009 and lasted five days. Average cycle between periods unknown... I don't pay attention, I had sex on June 3rd and June 19th. My first ultrasound estimated that I was 13 weeks pregnant and my due date is March 21st 2010 according to my doctor. So when is the most likely day I conceived and why is this not adding up. Could I have ovulated late in the month close to my next period which would have been late June. Help..