Hi, I felt the same way with my 2nd. With the 1st I wanted to show and it took forever, with the 2nd I started showing at about 12 weeks. I measured about 3 weeks ahead for most of my pregnancy. I think that my body was saying, Oh yeah, I remember this and out came the belly. I did buy a belly band and it made a huge difference on my back and legs.
Good Luck!!