If my 14 week ultrasound is on may 16th 2011 when are the dates that I concieved? How accurate is an ultrasound and what dates did I concieve

Depends. The ultrasound is very accurate in first trimester. If you are actually going to be 14 weeks by ultrasound dating on may 16th, then you would subtract 12 weeks from that day to find your approximate conception date.