everyone is different - there's no shoulds or should nots. I was showing, and this is my first, but then there are other girls here who werent.
I wouldnt worry.
I'm having my first & have been showing since about 8 weeks!!
There is another girl at work, having her 2nd baby & 3 weeks ahead of me & u cant even tell she's pregnant!
I wouldn't worry. It's normal not to show at that stage. I certainly wasn't, but happened to just pop at 16wks and then again at 18wks. I hated the 14/15wk mark - I really wanted a bump!
Give it time hun! Sometimes one doesn't show for awhile if this is their first pregnancy. True for me, and then with this one, I started showing at 9 weeks.