I'm 5" tall (or short) and I am 100lbs and very skinny. 

My stomach however, is quite pushed out all the time. It's not fatty, but looks almost bloated.

I can suck in my stomach and it looks really flat and proper.  

What might cause this? Or is it just the way I was made?

Are there any exersizes I can do to reduce this? I don't feel like working out helps because my stomach isn't "fatty" per-say. I'm really tired of having to remember to suck in my stomach especially in the summer when I'm wearing a bikini and it's not sucked it, it looks really bad.