Have you been constipated? I'm pregnant with my first and never imagined is be so constipated and therefore so bloated - I look quite pregnant too! It's too early for the baby to "show" in a first-time pregnancy - women show earlier when they've already been pregnant - as far as I can tell from the research I've done. I wouldn't worry about it - if it's because of constipation, see what you can do to treat that. (Gentle stool softeners like sennosides, dulcolate and Metamucil have helped me to some extent.) If that's not the case, I still wouldn't worry - chances are you're just bloated and because you're so thin, it looks like you're showing. (I'm no expert - just my thoughts!)
Oops - make that "docusate" (name of anti-constipation OTC med).
My first pregnancy I was showing before 8 weeks and I am a thick girl. I had a very noticeable bump. This pregnancy I'm not showing yet (I'm 8w3d). Since you are small, it's definitely possible that you are starting to show. Even though the baby isn't big yet, your uterus has been expanding and filling, and therefore you could be showing.
7 weeks is too early to be showing, at least showing the baby. It could be bloating, weight gain, and possibly twins/multiples. Your baby is too small right now,and where are you " showing" at? Your stomach or lower?