Alamak, sakit punggung masa first trimester memang common especially kalau second baby, uterus dia expand faster kali, plus ligaments da stretch from first pregnancy. Tapi since ini first time you're experiencing it, better la check with your doctor just to be sure everything's okay, especially since it's both sides. A few of my mum friends complained about the same thing and doctor dia reassure je, but I know lah rasa khawatir when something feels different, so jangan tahan, ring the clinic and mention the location and when it started!