Ay, normal lang yan sa pregnancy kasi ang muscles mo around your belly ay nag-stretch na at sensitive talaga, lalo na pag umuubo or sumisingā kaya parang nakakasakit, marami sa amin moms ang naranasan yan, especially around second trimester. But since you're 16 weeks and it's bothering you, better check with your OB lang para sure na okay lang talaga at walang iba pang concerns, kasi peace of mind din yan para sa iyo!