Since you're taking Vitamin D, you might also want to see if you need Zinc. Both Vitamins account for the largest deficits in the population. You might want to consider taking a Magnesium supplement since taking Vitamin D which can lead to a deficiency in Magnesium. Vitamin C is worth taking a few times through out the day.
The Trifecta is D,Zinc and C (with a magnesium supplement a few times a week).
I have read more than one study in the years past that consistent use of vitamin C supplements actually leads to a weaker immune system in the long term.
The Trifecta is D,Zinc and C (with a magnesium supplement a few times a week).