I have had 5 very successful live births and all of my children are happy, healthy and very intelligent. I have never taken a folic acid supplement. Sometimes I don't even take multivitamins and I have never taken prenatal vitamins since my first baby.
If you eat a healthy diet, I don't think there is anything to worry about. Even the cold cereal that you buy at the store is enriched with vitamins and minerals that they add, it's almost impossible to become deficient unless you really try.
The human race prospered very well long before it even knew that there was such a thing as folic acid.
Of course you can talk to your doctor if you are worried, but you shouldn't be worried at all. Don't think that you are stupid of you can't keep down a synthetic pill. It happens to everyone. It's best to get the nutrition you need from food anyway. Anything that the baby needs, he is going to take from you and you can catch up on what you need to when your stomach calms down.
Chances are, you have already been taking it without knowing it!! It's already naturally contained in food: here is a very handy link to all the foods that contain folic acid....and just proves that you're getting it even if you don't think you are

I'm sure your baby is bouncin' happy, do don't worry
http://www.ods.od.nih.gov/factsheets/folat
e.asp