Prenatals are most vital in the first weeks of pregnancy. Many women have went with out them and had normal babies. I'm sure you will be fine.
I am in the same boat. I took prenatals up through week 5 and by the time I got to 6 weeks, my "morning" sickness started. I am now 10 weeks and recently diagnosed with hyperemesis gravidarum, so needless to say I haven't been able to keep any vitamins (or much of anything else) down since then. Many people have the same problem and have healthy babies... I'm sure yours will be fine. Don't stress too much and just do what you can. Best wishes to you, and congrats - you're almost there!! :)
Same here I am 24 weeks and so far only taken 30 vitamins. I was scared and am but people say many people do this. I take them though still just in case.
I take them, but sometimes they come back up. I have pretty bad 'morning' sickness. But for the times they stay down, it's worth it to try.