You're not alone on Vitamin D supplements making you sick. I had very similar symptoms when I tried supplementing. Tested it on 3 different occassions, but each time I had a bad reaction.

Terrible insomnia
Flu like symptoms
Upset stomach that sent me to the bathroom
Anxiety - major
These symptoms took a few days to subside.

I just wanted to make my post to let you know that you are not alone, as I think a few others have reported as well that vitamin d makes them sick. I have since started taking fermented cod liver oil. Just started it three days ago so too early to report what it is doing, but it has not made me sick so far. I do not believe that vitamin d can be made in a lab, and that the vitamin d in supplements is somehow toxic, or can be to some people. We are all different you know? I am even considering looking for a milk that has no vitamin d added into it, because my reaction to vitamin d supplements were that severe. I too only took about 400 iu, or mgs. Very low dose, but again, I reacted severely.

I also told my Dr. about my reaction. She did not try to force the matter onto me after that, as I am the only person that can gauge my reaction, and what caused it. I tried two different forms of vitamin D supplements several times, and documented my reaction in a journal each time. I'm going for more natural routes to see if that gets my D levels up. Currently started the fermented cod liver oil, but also plan on trying chlorella. Praying that these sources work on getting my D levels up in a more natural way.