Oo, super normal yan mama, lalo na kasi kambal at 7 months na, ang bigat talaga! A few of us pregnant with twins dito sa circle, pareho lang ang nangyari, especially around this time when they're getting heavier. Try mo yung prenatal massage or hot compress sa likod, at pag matagal ka standing, umupo ka muna or maghiga with pillows under your bump para ma-relieve ang pressure sa singit at lower back. Pero kung ang sakit ay sobrang intense na o may ibang symptoms, better check with your OB lang para sure, especially pang-kambal pregnancy mo, para walang alalahanin.