There are some prenatal vitamins that you can buy over the counter, but you should ask a doctor if they are what you need. These might be better on your stomach, but they may not have everything you need. The prescribed vitamins may make you sick for a while, but it might pass after the first trimester has passed and your hormones have settled a bit. Those raging hormones are often the reason that some prenatal vitamins make some women sick when they take them. Some are lucky and don’t have any upset what-so-ever, but many more experience some when taking them.