With my first it wasnt until i was like 30 wks (no exageration) that i really started showing. All the clients had no idea that i was pg at all till then and they couldnt get over how far i was. By 40 weeks i popped out and it was noticeable but i really hid DD well.
DS was another story, around 12 wks i looked 25 wks. I ballooned out really early with him, it soon settled down though. I ended up all baby like with DD so that was good, no fluid build up.
This one, im 10 weeks and im showing a little bit. I think because im still B/Fng DS regularly that im still at my feeding body so i wont bulk up as such till he finishes. If he does. Im one of the lucky ones that drops a bundle of weight when feeding. I got to skinny with DD though so maybe not so lucky.

Its funny cause DD was a 9pd bub and DS was only 7Pd but with DD i looked smaller. Hope they keep getting smaller. I agree with the others though, different builds and different lifestyles play a huge part.