Prenatals 21 weeks

I'm a little worried that my baby isn't getting the nutrition it needs. Since I found out I was pregnant at 7 weeks, my doctor told me I can take two children's Vitamins daily instead of the prenatals that were prescribed to me because I couldn't get them down. But now I'm hearing different things from people saying that children's vitamins aren't doing anything for the baby 😢😩 any suggestions on a good prenatal vitamin? & is it okay to switch now? HELP!