I am petite - 5'4" 120 when I'm not pregnant. I gained 40 lbs with my first two pregnancies and am on the same track with this one.
I lost it all after my first, lost all but 5 lbs after my second. In my experience, the first 25-30 lbs literally fell off, w/o me doing much at all. It is those last 10 pounds that are a killer!!
Just so you know, your body will definitely be different after you have the baby. I'm not saying worse, just different. For example - after my first I was down to my prepregnancy weight, but some of my clothes just didn't fit the same. For me, my hips are a little wider now, they just never went back. And my tummy - well, lets just say that "muffin top" is a compliment!! I have to say though, that I never really gave myself or my body a chance to get back to normal. I was only not pregnant for 9 months after both of my kids before I got preggo again. So I'm sure if I really work on it and give it some time, things will go back (I have to tell myself that!!!!!!)
Don't stress too much about it. There isn't anything you can do about it now. Just concentrate on that perfect little miracle you are making!