I think it's just those third babies. They're ornery ;-)
I was sick as a dog with #3. Never threw up at all with #1 or #2,
but did it a lot with #3 all the way through 20 weeks.

Though didn't you have boy, boy, girl? So gender could have been the
reason? I'm not sure which way round it should be, I've seen convincing
reasons for both!

Cheers
Anne