Thanks for writing your query.
It will be helpful if you mention :-
1. Your Vitamin D3
2. Strength of Vitamin D3 in one tablet.
It seems that you are taking overdose of Vitamin D3.
Hypervitaminosis of Vitamin D3 can cause headache and nausea
You should reduce your intake of taking 3 tablets after discussing with your doctor.
Dose and strength of Vitamin D3 can be adviced after knowing your Vitamin D3 levels.
You can get Vitamin D3 in your body naturally, if you expose your body in sun even for few minutes daily.
I hope this is helpful to you.