Girls, how do you take calcium and magnesium? My doctor said they are…

Girls, how do you take calcium and magnesium? My doctor said they aren’t absorbed together, but yesterday another pregnant friend of mine was prescribed a calcium + magnesium vitamin by her doctor. Now I’m confused. Can they be taken together or not? I can’t stop taking calcium because my legs and arms hurt. And I can’t stop magnesium because I have uterine hypertonus. But for now, per my doctor’s prescription, I’m taking calcium (I’ll need to take it for two months). What do you think? How were these medications prescribed to you? And which ones?