Vit D is also needed to help with depression. Even feeling fatigued can be a symptom of mild depression. I mean the chemical type not the sort of day to day Woe is me, I can't cope type of depression.
The best thing is to continue taking the 2,000 iu a day, or even 5000 iu a day. Both these dosages are the recommended dose. For me personally if I go to 1,000 I feel crud, but 2k works for me very well.
Often lack of magnesium in the diet can cause similar effects and it is advisable to take some when on Vit D as well.
Low calcium, again, can have similar effects to yours. If you aren't taking a supplement it may be worth doing so. Many have Boron, and Magnesium added. Vit D's role is to help the body uptake available calcium, so if your PTH is up then provided you aren't prone to kidney stones, taking a supplement can help.
It might be best if you ask the doctor to run a full blood chemistry so you can see what you are deficient in, and work from there. It is always best to seek advise in these matters rather than self medicate.
Complicated, isn't it! Good luck!