Alamak, that's usually quickening lah, baby's movements! At 16 weeks some mums feel it early, especially if it's second pregnancy. Tapi since you're saying it sakit, better check with your doctor just to be safe, okay? Could be baby kicking, could be ligament stretching, or something else, best to get peace of mind from the doc directly. A few of my mum friends felt pulling sensations first before proper kicks, so don't worry lah, quite normal, tapi confirm with your OB jadi sure.