PLEASE READ: I'm super curious!! I'm 17 weeks pregnant, belly button is shallow and stretched out; BUT STILL NO NOTICEABLE BUMP!

I'm 17 weeks pregnant, I've noticed that before I was pregnant, my belly button seemed "closed" and "small"... at about 16 weeks I noticed that my belly button was opened and stretched out, and getting pretty shallow! My hole from when I had my belly button pierced is stretched and tight as well. I was wondering what this means.. I've heard that it's my uterus pushing against my belly button, I've also heard it's from the organs being pushed up as well... but my bump isn't that big yet and I'm sure my uterus isn't up that high yet. Can someone explain?