Wa'alaikum assalam sayang! Perut mengeras dan sakit pinggang memang common masa pregnant, tapi especially if it's one-sided atau persistent, please go see your doctor or midwife soon , jangan tunggu. Better safe than sorry kan, especially when it's your first pregnancy. A few of us mum friends experienced Braxton Hicks contractions (perut mengeras) around that time, but the one-sided back pain needs checking out properly. Could be ligament stretching, could be something else, doktor je yang boleh assess betul-betul. Don't worry too much, tapi jangan delay ye!