Wa'alaikum assalam sayang! Aiii, sakit pinggang memang common dalam early pregnancy sebab hormones & posture changes, tapi ngilu sebelah tu kena check dengan doctor sebab nak exclude anything yang perlu attention. Jangan delay ya, just give your clinic or hospital a ring today, suruh dorang assess properly. Better safe than sorry, especially dalam first trimester kan. One of my mum friends had similar and turned out fine, tapi doktor dia still kena scan to be sure. Don't worry lah, tapi do get it checked out soon okay?