vitamin D drops

Breast feeding mamas--do you notice any difference in your baby after using the vitamin D drops? I have been slacking on giving my son his vitamin D because every time I do it seems he gets really fussy after and gassy. Idk if it's in my head, but it sure seems to be a routine thing. How important are the drops? Stuck between not wanting to make my baby in pain with gas but also wanting him to be healthy with his vitamins.