With DS, my nausea started around 5 weeks, I think, and lasted about halfway through my second trimester. It wasn't terrible nausea, just persistent and annoying. I mostly had problems when I brushed my teeth, until a coworker clued me in about toothpaste flavor.
With my current pregnancy, I started feeling nauseous in my 3rd week, before I even got my BFP. I'm about 10.5 weeks now and still terribly nauseous, and vomiting multiple times daily. (I had gained about 7 pounds at this point with DS, and I've actually lost about 3 pounds this pregnancy).