My baby's due date is april 8th 2013 according to the 12 week ultrasound....I wanted to know when I conceived.?

Easy calculation. If your due date is accurate you can easily calculate dates. You look back 1 yr from the due date & add 12 weeks for the conception date.If the due date is april 8 that would put conception at july 1 of the previous year.If your due date is changed later, you can still use the formula to calculate.
July 16. Best estimate is july 16th plus or minus about 7 days either way... But then again, you should know!