I am 17 weekd and3 days pregnant my due date is December 10 I want too know when I conceved

Around 17 weeks ago.
Gestational dating is NOT exact and relies on available data and Best Guess.
If there is a potential paternity issue then a DNA test after the birth is the only surefire method..

From about 15 to 19 week ago, most conception dates are give or take 2 week. So there is no way to know, unless you only had sex one time. And of course no need to know a exact conception date, and no way to know, even if you needed to