Sakit pinggang di 12 weeks memang common lah, sebab perut dah membesar dan postur berubah, tapi lebih baik check dengan doktor untuk make sure everything okay, especially if it's sharp pain atau accompanied by bleeding atau contractions. A few of my mum friends dah experience the same, some kena adjust their pillows, pakai maternity belt, atau just more rest je langsung hilang. Minum plenty of water, try to sleep on your left side, dan jangan angkat benda heavy. Doktor akan tahu what to do based on your situation, so jangan segan to ask during your next check-up, okay?