It really varies. I'm still very, very sick, but I was also on a prescription for my nausea (until a few days ago...I needed to stop taking it because it made me too foggy headed and I couldn't take any more time off my work -- and, puking is less disruptive than being confused in my line of work).
With my first kid, I felt all the way better around 16 weeks, but was really sick through 15 weeks.
That said, I think the responses in this thread are a bit atypical, and most people really do start to feel better around 12ish weeks. Fingers crossed that that will be the case for you!