The neutrophils are not the only cells in our body which are responsible for our immune functions and body resistance. The other mechanism in our body to prevent infections are;
1) Other white cells, like lymphocyte.
2) Immunoglobulins which are proteins for immunity.
So if your white blood cell count is normal, there is no serious risk, or worry of infections, especially if you have not been identified by immune deficiency disorders. The cell count like absolute neutrophils counts are very variable and do change in just couple of days or just in a week, so this may improve in few days.
A vitamin D deficiency is also not very concerning if your bone mineralization is normal. Vitamin D has its greatest effect on the maintenance of adequate levels of serum calcium, which affects the bone mineralization. Bone mineralization (detection of osteoporosis or osteopenia) is seen by an investigation called as bone densitometry, which predicts the risk of fracture of bones and strength of the bones. It is good that deficiency of Vitamin D has been detected and you should take Vitamin D supplements. The other good thing is that it corrects very fast. Because the sun does not rise high enough in the sky in the winter months, people who have less sun exposure require more dietary intake of vitamin D. Again, you should not be terribly concerned by the deficiency and you just have to keep taking the supplements of it and calcium and monitor it's level.
Please feel free for your follow up questions.