I just found out i'm 4 week they did some blood test on may 23 so what i want to know when did i get pregnant?

Get an early u/s: The most accurate way to know when you became pregnant is to get an ultrasound that measures the crown to rump length of the pregnancy between 7-10 weeks. That is accurate to +/- 3 days. At 4 weeks, the measurement of the sac has an error of +/- 7 days. So there is some error in dating. If you were 4 weeks 5/23, You probably became pregnant around May 9 give or take a week.