Ay sis, yan talaga common sa late pregnancy, yung heaviness ng tummy plus the back pain combo is real, lalo na at 30 weeks ka pa lang so mas lalaki pa yan! A few of us had the same issue, and honestly it's usually just the weight plus hormones loosening everything, but since you're having difficulty moving, better check with your OB para masiguro walang iba, like constipation or something more serious na kailangan i-address. In the meantime, try pelvic support belts (nakatulong sa iba namin) and do gentle stretches, but definitely mention it sa next checkup mo ha!