Talk to Gynecologist on Vitamin D

In my earlier 2 pregnancies when I had extreme pain in legs Dr prescribed sunny d soft gel capsule to me and it worked both times now I have my third one month old and same pain as before can I take vitamin d capsule is it safe because I breastfeed my baby? Also in earlier 2 kids Dr didn't prescribed vitamin d for my kids and we live in flats with no sunny side... can I give vitamin d drops to my 5 and 7 years old as well?