Suggest you get a Vitamin D3 blood called a "25-OH Vitamin D3" test before taking additional Vitamin D3 supplements. Then decide on the amount of Vitamin D3 and have another test after a few months.
Check with Mercola.com for the OPTIMUM Vitamin D3 levels.
My Vitamin D3 level was on the low side even living in a sunny climate and taking a multi-vitamin with 400 IU of Vitamin D3. I increased the intake by another 800 IU per day (Puritan's Pride) and after about 3-months my D3 level is at the upper optimum range.