I recommend a prenatal vitamin from New Chapter called Perfect Prenatal. They make an organic line of products that I use and enjoy. The supplements are derived from whole, organic foods. You can purchase these at stores like The Vitamin Shoppe, Veria Wellness Center, Central Market, or online.
I used these and loved them. I never had any sort of side effect like upset stomach or headaches. They are expensive, but as with most things, you pay for what you get.