I have noticed the same thing with this pregnancy, and it's also my second child...first I thought I was just bloated but it never went away, I'm just getting bigger, and I'm only 17wks... I was told that now since it's your 2nd child your body already knows what to do, so you'll get bigger and start to show earlier...my Dr said it's normal too...so I'm not worried. Plus i gained 11 pounds already. And it's not that I'm eatting a lot or anything.
I'm 5 wks and am bloated as hell this is my second as well
You could also be a bit bloated. I got bloated at the beginning and my pants didn't fit but it subsided so I can still wear my regular clothes.
Your second pregnancy will cause you to start showing earlier since your uterous is already stretched out.