Salam! Sakit belakang masa pregnant memang common, lagi-lagi bila dah masuk trimester kedua macam sekarang, sebab perut dah membesar dan postur berubah. A few of my mum friends experienced the same around week 19-20, tapi kalau sakit tu quite bad or getting worse, better check with your doctor or midwife just to be safe ya, diorang boleh assess whether it's normal pregnancy aches or something else.