i think its the one night stand.. we have the same due date..
From a conception calculator: (keep in mind that this is only accurate if you got your due date by ultrasound in the first trimester)
Probable Date of Ovulation: January 3, 2013
Possible Dates of Conception: December 30 to January 7, 2013
Due Date: September 26, 2013 (40 weeks)
Where did you get the count of 15 weeks pregnant? Was it by ultrasound? If so, when was the ultrasound and how far along were you then?
The one night stand. I'm 14w 3d an my baby was conceived after Christmas. Your further then me so if would have been before January.