I have fibromyalgia, and i was low in vitamin D as well, i have to take one pill per month, i missed it one month by error and my results showed i was still low in it, so obviously it is important not to miss a dose.

Yes get it sorted, being low in Vitamin D can be potentially very harmful to you.

Good luck with it all, and keep us posted how you go, hoping your pain eases to a bearable comfort or just goes away, i know that is unlikely to happen, but we can all wish can't we?