Conception Date-I cant Believe Situation I put myself in

[bigdummy3343]

I just had a sonogram they told me my conception date was give or take 3 days April 28th making me 5 1/2weeks along last Wednesday, June 4, 2014.
  I had sex with a New man on May 24th without protection.  So basically there is a 17 day difference in my long term boyfriend and the basically one night romance man., whatever you want to call him.
I ask the ER doctor if it was possible if  I was 12 days pregnant by the May 24th guy, she told me no, you are 5.1/2 weeks which makes it my long term ex-finance, but here's why I have questions, we tried for a year straight to get pregnant and was not successful.  He does have a daughter by a prior woman but was told he had a very low sperm count and he never got me pregnant in that whole year, and I have also been reading the internet which has me freaked out.  I know my last period was in april but the exact date, I couldn't tell you, I know it was around the 15th and 23rd of april.  
I just DONT WANNA END UP ON MAURY if there is a likely chance I could be pregnant by the one night stand I do not want to go through with the pregnancy at all, because honestly I could not live with myself knowing that I was so irresponsible.  

Any suggestions or opinions would be helpful

[katyrb]

Early ultrasounds are pretty accurate, If they told you that youre 5 1/2 weeks along i don't think that you have to worry at all. That's a huge gap between the dates. Just because your boyfriend had trouble in the past doesn't mean that he couldn't get you pregnant. Don't worry!

[AnnieBrooke]

I agree with katy.  17 days between the guys is enough time for a fifth-week ultrasound to be accurate.  If you had an early ultrasound and the guys were three days apart, that would be problematic.  But not when they are 17 days apart.  Trust what your doctor says; if you don't trust the ER doctor go to your regular ob-gyn and get another ultrasound.