I'm not sure, sorry.
Your belly will probably just pop-out one day. Some people carry/show differently and at different stages.
This time I was showing early, but with my DS I didn't show until later on.
If you're worried about your weight gain ask you OB or midwife.

I've only gained 6kgs so far in my whole pg.
I get weighed at each OB appointment, and he said that it was fine.

I hope you're having a H&H pg.

xx