Wa'alaikumassalam! Generally most airlines allow pregnant mums to fly up until 36 weeks, tapi some are stricter and cut it off at 32 weeks, best to check with your airline first since policies boleh berbeza. For a Sarawak to Johor flight, confirm with the airline you're planning to use, and maybe get a letter from your doctor just in case they ask (a few of my mum friends kena mintak dokumentasi when flying in the third trimester). If you're still in the earlier weeks it should be fine-fine je, but safer to double-check sooner rather than later!