On top of prenatal vitamin, is it safe to take more vitamins like b complex, vit d, omega 3?

Yes, in fact wise: No prenatal vitamin has adequate levels of vitamin d. Adults in the winter months need to take 5-8000 iu of vit d3/day to achieve optimal levels. Additional b complex is perfectly safe as long as total b6 does not exceed 200 mg (highly unlikely). Prenatal vitamins do not contain essential omega 3 fatty acids, important not only for your health but the health of your baby if you become pregnant.