Believe me, there are many factors that influence how much you show and how early.
I didn't really start showing until about 7 months and even then it was very little. Now that I am entering my 9th month, I have had some people at work come up to me and say, "gee, you're pregnant, I didn't even know"... and when I tell them I am due in April, they are shocked. I am very tall and had a bit of a belly to begin with, so that impacts it alot. And my baby is not measuring small at all, it was estimated to 6lbs at my last ultrasound 2 weeks ago
Plus how the baby is positioned makes a difference.
It's still very early for you. I wouldn't worry about it, there's still lots of time for that belly to grow