You're better off just taking magnesium. Most people get enough calcium (if they eat dairy) but you need magnesium as well to activate the calcium. Don't think the vit D, would upset your tum, but you should only need it through the winter (unless you don't get much summer sun). Make sure you get a good quality magnesium supplement (try Healthspan) and if necessary take half morning, and half evening to prevent the runs.
There have been lots of reports of late saying that calcium supplements are not effective and can cause problems such as gall stones. I would do some internet searches and then decide after you have more information.
