However, you have the added burden of being intolerant of one of the best sources of calcium. Therefore, it is good that you are taking supplements. Between the foods you eat and your supplements, you should aim to get around 2000 mg. of calcium daily, especially during the last trimester. Be sure to avoid the natural source calcium pills such as those produced from oyster shell or bone meal. They are apt to contain lead or other toxic metals.
Calcium interferes with magnesium absorption, so take additional magnesium.
It is not critical that you take the magnesium and calcium together. I recommend 500 mg. of magnesium for every 1000 mg. of calcium. It is best if you take the magnesium supplement in smaller doses throughout the day, since the body can only absorb a small amount at a time. By the way, studies reveal that women who supplement with calcium during pregnancy have a reduced incidence of high blood pressure and preeclampsia. Watch this report about showing affection to boys.