Calcium and magnesium work opposite of each other in the muscles.

Basically calcium enhances contraction, and magnesium relaxes.
The occurance of severe twitching suggests to me this balance is out of whack for you Aussie.

So stopping both (you probably get calcium in the diet already), will reduce the calcium at least. Some twitching may remain unless you eat magnesium rich foods for the stopping period. For example. 3 oz unsalted almonds have 270mg of mag... almost a whole RDA in fact. I have other food examples on that thread.
So try to eat wisely and get your mag that way.

Then after a couple or so weeks, bring in a good mag supplement (one without oxide in it) and see what happens. The Linus Pauling Institute has monographs on both calcium and magnesium to give you ideas about food choices.
Just Google them, and click on their website and put each one separately into the search box and it will bring up lots of info.

If nothing changes then when you stop both minerals, and you are eating wisely, then you have that information in hand for any neuro visit.
Also it might be useful to keep a diary... journal....containing what you eat all day at what times, and when the twitching is worse or better. This will show if you have blood sugar problems, or food intolerances.