Sakit pinggang sebelah kiri memang common masa pregnant, sebab baby growing and hormones relax ligaments, tapi at 30 weeks better check with your doctor to make sure it's nothing serious like kidney issues or ligament strain yang kena treatment. A few of my mum friends had similar aches, some kena physiotherapy or just rest + warm compress memang hilang, tapi every pregnancy berbeda so best lah get it checked out okay? Jangan worry too much, usually normal je, tapi doctors will put your mind at ease.