When did i conceive?

Patient: Hi, Hope you can help, I am pregnant and i have been given a due date of may 21st 2011. I had sex on saturday the 21st of august and again on saturday the 28th of august. I was bleeding a few days before the 21st of august and had a light bleeding a day or so after. The reason im confused is i am due on 21st of may and i had the morning after pill in the afternoon of the 30th of august. when do you think i conceived?

Doctor: You probably concieved during the time period august 24- September 1st, keeping in mind that this is calculated accordin g to a normal menstrual period of 28-30 days.Since you were sexually active on the 28th of august and took the morning after pill only on 30th the chances of preventing the pregnancy were low.