my labs: vit. d 25-oh- D3- 23 and 25-oh D2 <4.

I understand the difference between them- but what is the significance of having such a low amount. (especially the D2). I know that i need supplement, but wondering why the D2 is so low. How are these tests evaluated by the doc. and/or they both used? I am going to the doc next week but wonder if anyone knows. I have been googling but not finding the answers
thanks in advance