I know this isn't exactly rational, but....
With my last pregnancy, the m/s started at 6 weeks on the nose. And didn't ease up on me until 22 weeks. Tomorrow I will be 5 weeks and 6 days. I have in my head that it will be my last pleasant day for the next several months.
I know, I know, every pregnancy is different. Told you it wasn't rational.
ETA: but I'm ready and armed with B6 and crackers and lemonheads!