What day did I conceive?

Hello,

I'm new to this website. I just have a question. My husband and I only see eachother on the weekends with both working schedules and It was around Christmas time we think. I took a test around January 18th and it said positive. I went to the doctors and they said with the sono it said I was about 5wks along. The only thing is that I got my last period Nov 29, 2008 and I go 6wks for my periods. So I was due to get it January 10th. So I am still not getting an answer to my question when I go to the doctors. The one doctor said it looked liked I had an estimated due date of Sept 28, 2009. Please help if you can. Thank you.