Normalnya belly size varies betul, some of us show later especially if it's our first pregnancy or kalau kita naturally petite! At 19 weeks you should probably still be quite small because baby is still quite tiny, so jangan worry too much lah, my friend kami pun at this stage people couldn't even tell she was preggy. But best to mention it to your OB/gynae next visit just to make sure everything is tracking okay with your scans and measurements, because they'll have the clearer picture of your baby's growth! Every mum carries differently, honestly.