I am 33 weeks 4 days pregnant, the dr has given me a due date of april 17, 2013 based on ultrasound. when is the most probable day/days of conception?

Subtract 2 weeks: When "calculating" this, we assume a 28 day cycle with ovulation on day 14. So obviously, it is just an estimate. To get approximate conception date, subtract 2 weeks from your current gestational age. That will then be how many weeks ago you conceived. So in your case, your date of conception is approximately 31 weeks 4 days ago.