I have irregular periods. my last period was june 18th an ultrasound today said im 6 weeks 2 days. i had sex august 24 & sept 5th. when did i conceive?

August 24th: August 24th would be the more likely date. Based on my computer calculation the "average" day of conception would be 8/26, which is very close, of course, to 8/24. So if you only had sex on 8/24 and 9/5, then definitely the 8/24 is the correct date.

August 25: Your estimated due date is around may 19, 2015. Your last menses if regular would occur around August 12, 2014 making conception around 8/25/14. Congrats and good luck.