I used to have this problem too with women's one a day, and when I asked my doctor she said if a vitamin is making a stomach upset then thats your body saying it doesn't want something in that vitamin (some vitamin or mineral is too concentrated for you body). So I switched until I found one that didn't upset my stomach. I found a one at whole foods that works well but also they make adult chewable gummies which dont seem to upset stomachs as easily. Or you can actually take 2 flinstone vitamins if you want.
P90X : If you were able to look inside of your cells and see your "good" enzymes increasing, your energy-producing mitochondria multiplying, your cholesterol falling, your arteries clearing, your blood vessels becoming more efficient, your muscles strengthening, your bone-density improving, and all of the remarkable changes that this program triggers, it would be clear that the scale and calipers are just insufficient ways of measuring success.