I got to that weird stage where you couldn''t tell if I was pregnant or fat at 17 weeks. By the time I hit 20 weeks is when you could really tell.
I didn't start showing until about 17 or so weeks. My boyfriend was in denial for the longest time because of it lol. Now I'm 21 weeks and their is no denying it now (:
If it's your first baby people will probably notice around 17-18 weeks. You will probably notice a difference 13-14 weeks.