For some women once your body starts to prepare to have the baby you will get sick again. It happened with all 3 of mine. I'd ask your doc to check and see if you are dilating.
Try keeping lemons in the fridge. Whenever you feel sick go get one and smell it. Weird I know but there's some kind of calming effect that it has.
If this is your first and you want more tips on how to deal with nausea just pm me!