I know that people say the symptoms can't possibly come on before the period is due. But I know that's not true. I've been pregnant 7 times with 3 miscarriages and 4 daughters. My husband and my father and others in my life knew within a week of conception. My nausea, light-headedness, emotional behavior, and some other symptoms started within 4-5 days for me.
My last pregnancy was the most dramatic. Within days my boobs hurt so bad I wanted to cry from the pain. I was hot one minute and freezing cold the next. Acid reflux started almost immediately and the round ligament pain was bad from the very start. It was just pretty well a sure thing. I conceived on the 2nd of the month and by the 11th I had my positive pregnancy test already.