Also I personally have not found a calcium supplement that I absorb so I started to make my own in the following way-I juice three or four lemons and then pour it over three eggs (whole, white shells, uncooked). I let it sit for two days and then I take anywhere from 5-10 teaspoons per day. Eggshells contain many other trace minerals that help with the absorption and assimilation of calcium. The lemon minerals help too plus the acidity helps aid absorption.
Have you tried decreasing the acidity of your mouth, like sucking on xylitol mints (decreases bacteria)?