My D has been low for years. Low vitamin D is associated with a condition called secondary hyperparathyroidism. This is where the parathyroid does not work right and the body also does not absorb calcium very well because the parathyroid tells the small intestine not to absorb calcium. It is a way the body thinks it is protecting itself. One test that is usually done to check the parathyroid os a blood test called PTH Intact. This will measure PTH (Parathyroid) and also tests your calcium and serum ionized calcium levels. This helps to determine if the parathyroid is effected but someties it is even with readings close to normal. There is a medication that is a form of Vitamin D 1, 25 hydroxy that is used to help lower PTH levels. Your case may be a bit different. Good thing you have an Endo that will help with this.
I also suffer from malabsorbtion with many vitamin deficiencies. I have trie the supplement route and my levels are still crap. I now get Multi-Vitamin Intravenous Infusions. This was just started at 1 time month but is being changed to one time week. They are also adding extra vitamin C, Vitamin D, and Calcium to my infusions. I had gastric bypass surgery in 2004 with complications since day one one. It is believed I developed what is known as short gut syndrome where the small intestine was shortened for surgery somehow should have still worked okay because only a smaller area was bypassed and the area left sort of stopped working.
I wish the best for you and hope you feel better soon. If you have any questions I will share more if you need on my story.
Also can read more under the heading under Skin titled Weird changes in my nails
mother1991 aka christina