I've been taking Vit D regularly for maybe two years now and I still get low Vit D tests back. It seems to fluctuate quite a lot. Even last summer when I thought I was getting loads of sun in the UK (relative to normal UK summer) I still tested low Vit D.
That sounds strange. Low as in lower end of recommended range?
2000 IU should get you a pretty good level, that is then topped up by exposure to sunlight
hippy
Simba
That should get you to optimal levels pretty fast!
https://nutritionfacts.org/video/the-optimal-dose-of-vitamin-d-based-on-natural-levels/