When in doubt always consult your gynae. If they say everything is ok, then don’t worry about it as every pregnancy is different. I’m gaining a lot of weight starting 1st trimester, even though i did not eat more. My tummy is looking more like 8months then 6. But the gynae said baby is ok, my weight gain is moderate, no worry. Similarly for you. Don’t worry, when you doubt always consult your gynae they know best. Take good care. A happy mama, a healthy baby. God bless you and baby.
Normally you get around 12kgs during pregnancy'. belly is not showing at 19 weeks is normal. You can monitor baby's growth during check ups.