Mmmm, I'm a 16 and although people kept telling me that I was "tiny" for how far along I was, I still looked obviously pregnant with both bubs. DD was 3.9kg, DS was 3.3kg
Actually, 6 months after having DS, i still have a baby belly. When I took my dog to the vet the other day, the vet remarked: "Oh, you look like you have another one on the way" ahem, no, I'm not, but thanks! I thought these situations only happen in comedies...

The size of your belly depends on your pre-pregnancy size, the baby's size, baby's position, width of your hips, location of placenta, amount of amniotic fluid, your posture etc.

I understand that you want to look pregnant. I looooved my belly. For once in my life I had a good reason for having a belly