Hello, I Was Wondering Why I Had Such Horrible Allergic

Hello, i was wondering why I had such horrible allergic like symptoms when I took Viitamine D3. I began taking Natural Factors VitD3 a couple weeks ago and then began with very strange symptoms which a pharmacist told me was an allergic reaction. I had a hard time breathing, began with a bad rash around my neck, I was dizzy, horrible headache and bad muscle pains. I stopped taking it and started a different brand but the same thing happened. I got my blood work done to check my levels and my VitD was very low....32 (normal range is 75-200). Can you help?