I started to show really early!
I was really thin before I fell preg with first bub so it was really noticable around 3 months.
I had big babies as well so i dont know if that means anything.
But i know ppl that dont show until around 20wks....it just depends on the person i guess.
My friend didnt show till she was over 30wks....but she is really tall so she could carry abit of extra wieght and look normal