Don't sweat it . I'm 4' 11 and about 105 pounds when I got pregnant with my son and I didn't start showing until I was about 5 or 6 months. Everybody is different and if it your first pregnancy it may take longer for you to show
I am 5'4" 115... so a little bigger but I didn't show with my first until 30 weeks. If you are concerned just talk to your OB. :-)
In about 11 weeks and my tummy is already rounding and showing but im also petite. Everyones body is different so dont be worried! :)
Its very normal my girl friend is having her 1st kid n she's 3months now she's just starting to show !