Is it possible to have a positive pregnancy test at a little over 2 weeks pregnant?

From what I calculated I should be due April 18th. I saw my ob yesterday and he calculated April 26th. Which means I found out I was pregnant at only 2 weeks and 5 days. These dates do not seem right. I'm either wrong about my period (which is possible because I have not really have been regular or had any bleeding at all since I'm 6 months postpartum)or I feel like I'm farther ahead. I got blood drawn yesterday, so hopefully we will get some insight.