I'm 127 pounds and 19 weekd pregnant why am I not showing? #1st time mommy

Depends. How tall are you? Are your check ups ok? Us okay? Then you may just be carrying the baby deeper in the pelvis that most and this could be a normal variant. You may have good, tight abdominal wall muscles. If this is of concern, discuss with your obstetrician and get reassurance or evaluation. Probably just a "you" thing and normal! good luck and happy motherhood!
All different. If pregnant, you will show sooner or later. Enjoy the tiny belly while it lasts. As long as your checkups are good...