I think everyone is different hun. Ho ever you are you are normal for your own body ATM for either twins or not....who knows maybe triplets????

My girlfriend is preggers with twins and 13wks at that, and no sign yet really, just a tiny tiny bump so far. And she has had 2 pregnancies before, both tiny too.
My two pregnancies on the other hand have been HUGE!! and the second time quicker then the first. Just genetics sometimes too, our family retains alot of fluid during our pregnancies.

Sorry about the BLAH BLAH.
HTH
In general you do get bigger earlier with twins and feel even more nauseated and m/s all day etc double the hormones and bub space.