Ahhh sayang, back pain at 7 weeks adalah very common dalam early pregnancy, hormones kita dah start producing relaxin which softens ligaments, so the spine area gets stressed even though baby still so tiny lah. A few of my mum friends complained about this around the same time, especially kalau kerja standing or duduk banyak. Best lah u check with your gynae to make sure semua okay, tapi meantime try to maintain good posture and maybe use a pregnancy pillow when sleeping, it really helps!