Pregnancy Vitamins!

Hi All, im currently 10 weeks pregnant and my doctor put me on Pregnacare Vitamins with Folic Acid but they make me feel like crap! It makes my nausea worse and this maybe TMI but its turning my poo black because of the Iron. It worries me when I see its black as ive always had problems with my stomach! So my question is, has anyone had these before? And would it be ok to stop taking them but continue taking Folic Acid Tablets? Im tired all the time and never have any motivation to do anything! Please help! :(