I take malic acid/magnesium supplements along with calcium and lots of vitamin D3. It does help me with my pain and fatigue.
Check out the Fibro 101 thread...the first thread on the forum. There is a link in there all about malic acid/magnesium supplements, how you should start out taking them, and how they work in the body. There is a second link about vitamin D, too. These links could answer your questions.
I'm glad you joined in and I hope to hear more from you soon.