To cut a very long story short, it seems as though my persistent headaches have been primarily caused by NutraSweet.
Several years ago I was on holiday in Israel and noticed a warning on the cans of Diet Coke. The warning advised not to consume more than a given amount of NutraSweet per week.
I contacted the providers of NutraSweet in Australia when I got home, and was told there was absolutely no problem with it. I now realize (after much pain and discomfort) that this is simply not true.
I am very concerned that the medical authorities in Australia have put almost no effort into screening out potentially harmful additives such as NutraSweet.