21w0d preg when did i possibly conceive? lmp 3/28(regular 28 day cycle) june 3rd 8w1d u/s changed edd to january 12 (10 days later) going by that now!

Reverse calculation: With a due date of January 12, 2015 - the ovulation date would be April 21, 2014. The ultrasound was performed at 8 weeks and 1 day so the range of error would be about 4 to seven days. Since you would have conceived on the day you ovulated - that would have been April 21, 2014 - including the range of error for the ultrasound means ovulation and conception would have been between April 14 to 28