I take a b complex and vit d and noticed my first day menstrual cramps decreased drastically. cramping still, however very tolerable. ok to continue?

While the B and D: Probably have had no effect whatsoever on your cramps, they are both very safe and there is no reason to stop either one.

Of course!: Such a quick benefit might be related to the b complex, particularly vit b6 which can help relieve cramps. Magnesium (ideally as mag, glycinate or taurate) also often helps cramps. Vit d is esp. Beneficial in fall and winter months but wise to take year-round if you use sunscreen or don't get much mid-day sun- most adults need 5-8000 iu/day to attain optimal levels.