I was listening to a podcast interview of Chris Masterjohn and he mentioned, almost in passing, studies that were conducted, in the 40's, I think. TO make a long story short they found that high doses of vitamin D could be toxic, and that high doses of vitamin A could be toxic, but when you combine them together, the toxicity goes away. There was also a role to play for K2 in this scenario. He said that he wasn't sure what the ratio should be, or it could be just that a certain amount of each is required to nullify the toxicity.

Anyway, if vitamin D3 causes this reaction, there is obviously something wrong. Could it be an allergy to something the Vitamin D3 comes in ? I think they typically use soy oil, lecithin. Try a different brand?

Or consider getting your vitamin D from the most natural source... sunlight.