Sakit pinggang sebelah kiri memang boleh jadi normal dalam early pregnancy sebab hormon dan perubahan postur, tapi since you're only 5-6 weeks, better check with your doctor je to make sure everything okay, especially kalau sakit tu quite bad or continuous. A few of my mum friends pun experienced random back pain early on, but everyone's different so best to get it confirmed. Jangan worry sangat lah, tapi jangan delay the check-up either!