Hello, I would be happy to help you with your question.
1. Based on your due date of 10/27, then conception occurred right around 2/3/2013.
2. Based on your LMP, though, conception would have occurred around 1/1/2013
3. Based on the 3/20 scan, your due date is 10/31, with conception around 2/7
Given the lack of reliability of your cycle, the most accurate dating of the pregnancy
(and conception) is the ultrasound
. At about 8 weeks the ultrasound is very accurate. Based on that scan, 'ManB' is the father. Also, your due date should be 10/31. These facts should be further reviewed with your doctor to confirm what I am telling you.
I hope that this helps. If you have more questions, please click on "ASK ME A QUESTION" link above to directly ask me a question!