I've heard similar complaints from friends about the metallic taste with certain multivitamins, and it's actually quite common. Try taking it right after a meal or with a strong-flavoured drink like orange juice to mask the taste, and some mums find taking it at night instead of morning helps because you're less likely to notice it. If the nausea gets worse or you can't manage it even with these tricks, might be worth checking with your PD or asking the pharmacist if there's an alternative brand that sits better with you, since you do need the vitamins especially if you're pregnant or breastfeeding.