Prenatals the WHOLE pregnancy?

So I'm almost 16 weeks along and I've been nauseous and miserable the whole time. I accidentally skipped a prenatal the other day and felt amazing! So I tried another brand and it made me nauseous, too. Skipped another day, and felt great again...so, do I have to take prenatals the whole pregnancy? Or can I stop once the first 3 months is up? Also, before I get hateful comments, I do love my baby and want what's best for it, so if I need to keep taking them I will. lol