Stopping anti-nausea meds

I've been on Diclegis since about 9 weeks (17 now) and I thought that since I've been feeling so much better I could just stop taking it. That was a bad idea! The day after I skipped a dose, I felt awful and threw up. I've been taking it since that day and feel just fine. Also it's pretty expensive (like $100 after insurance) so I really don't want to have to get a refill!
My question is: when did you stop taking Diclegis (or a similar anti-morning sickness med)? Did you stop cold turkey or does the dr advise you how to wean yourself off of it? Or do you take it the whole pregnancy?