Im experencing the same problem. I finally got my calcium test kit and found that my calcium level was down to 280. I have started adding supplements to increase the levels, now that i have a test kit.
Ive also read that with depleated levels of magnesium can also cause this problem , Im still wiating on my test kit, but I suspect that my levels are low. will not dose to much mag  without a kit, but these are parameters that you can check.
Beyond this I cant help.
Good luck and I hope this helps.
Chris.