Best vitamin for period pain/mood? Currently only taking vitamin D3 1000iu & vitamin b complex

Depends. Different items work for different people, but many patients report a better sense of well being with a b complex vitamin, and with significant vitamin d. Depending on your latitude and sun exposure, you may or may not get enough vitamin d from sun. You could consider trying 3, 000 iu of vitamin d. Also there is some evidence to suggest that methyl folate also helps improve a person's mood.