Tri-Vi-Sol is often easier on them than Poly-Vi-Sol. Try that.
You give vit D (or something with vit D in it like those mentioned) from birth for as long as they are BFing or until they start taking a multi-vit as a toddler.
You can also make sure they get a bit of sunshine everyday so they can make vit D for themselves.
Some feel strongly that as long as mom has extra/enough vit D in her diet, baby doesn't need vit D.
So, it's up to you, really.
I've not heard of iron being recommended before. That is probably because breastmilk isn't loaded on iron. But baby has enough in stores to get them safely to 6-9 months before they need it in their diet. By then they should be eating enough solids that they get their iron that way.