When I was younger and didn't want to get pregnant, I would obsess over every twinge of nausea, thinking I might be pregnant. But I later learned that nausea isn't necessarily the first of the early pregnancy symptoms women notice.
When I did get pregnant the first time, what I noticed first were breast changes. I would always get a little sore before my period, but that time it was just a bit different. I didn't experience any nausea until I was six weeks along, so two weeks after I found out, and even then it wasn't very serious for another week or two.
The moral of the story is *not* to obsess looking for early symptoms. Know your cycle, know when to take a test.