I'm taking Pregnacare too, but I don't think the vitamins necessarily help with tiredness. Not sure. I still have that 'I could put my head down anywhere, anytime and SLEEP' tiredness that's not yet easing off.
I started taking the vitamins instead of just folic acid when my sickness started because I was really worried about not keeping anything down. I don't know if it helped, but I take them religiously at bedtime just in case.