Hi, Promise, we don't do judgement here on the DNA/Paternity forum.
Here is what the conception calculator says for a due date of September 12. If you got the due date from an early ultrasound, the first guy is not the father.
First day of last menstrual period: December 6
Probable date of ovulation: December 20
Possible dates of conception: December 16 to 24
Due date: September 12 (40 weeks)
How did you get your due date? If it was from a calendar or a little cardboard wheel, it's not as reliable as if it was from an ultrasound, and if it was from an ultrasound is it less reliable as the pregnancy progresses. But if you got the due date from an ultrasound in your sixth week, you are in good shape (except for your guilty conscience). Six weeks "pregnant" as told to you by a medical person (doc, nurse, ultrasound tech) means 4 weeks since conception. By the count of six weeks, you conceived around December 21, and from the ultrasound (if you did have one at six weeks) you conceived around December 20.
When I went on January the 21st I was 6 weeks , I got my due date when they asked when was my last period witch was back in December , so if I had a period after me and that guy had sex the following month in December that makes the baby my boyfriends ?
I can't actually understand the part of your questions that says "if I had a period after me and that guy had sex the following month in December."