the last few months I've been constantly weak, although sometimes its worse. I've also had some muscle shaking and twitching. Been to neurologist and the MRI was fine, I of course am worried its neurological, but I have to try and fix these deficiencies. Is 13 for Vitamin D (whatever that means) level low enough to cause these symptoms? I'm female, age 18, 109 lbs, and 5' 4'' thanks!