When will my belly get hard

Hillary
This is my second pregnancy. My first one was five years ago and honestly don't remember much. I was super small and my belly was always hard from the ab muscles so I don't remember noticing when it got hard. 
I'm 13 and a half weeks and when I stand I notice it being a little firm. But when I lay down its squishy. It makes me nervous like I'm not progressing. 
Is there a general time span of when it gets hard and defined it is it just always different ?