28 weeks and...

Kat
28 weeks today, and for the first time my baby bump got distorted and I'm pretty sure the little round bump above my belly button was his butt sticking up in the air! Is this early to see this?? 
Or normal? 
I feel stupid asking, I probabaly should just be happy he's an active little one but I'm curious about size because I have GD. Wondering if he might be a little bigger than normal. 
Ultrasound tomorrow!