Do you need an endocrinologist for very low vitamin d (blood test=10) w/ strong symptoms like fatigue, muscle aches, anxiety, general weakness?

Depends: Not absolutely essential, as family practice / internal medicine can initiate treatment, and as long as respond, no problem. If complex / delayed response, then endocrine can help.

Not Necessarily: If there are a multitude of medical comorbidities, an evaluation with an endocrinologist may be helpful. Otherwise, a general practitioner or psychiatrist can manage vitamin D deficiency.