Ah, I get it, this can be worrying lah even though you're eating fine and no morning sickness! Every body is different, some mums gain slower at first then catch up later, especially if you started at a heavier weight or your metabolism is just faster, honestly at 16 weeks some mums haven't gained much yet either. Best to just bring this up at your next checkup so the doc can track your baby's growth and make sure everything is on track, then you'll know for sure if it's something to worry about or just your normal pattern.