How can I shrink my stomach?

I have a normal bmi: approx:24.0

but I have a big stomach, I look normal otherwise, but I look like I'm a bit pregnant if I don't hold my stomach in. so I was wondering how to go about losing it so I can get a flat tummy, and about how long it would take?( by the way I know all about eating healthy, drinking 8 glasses of water bla,bla,bla, and I'm already doing it)
How can I shrink my stomach?
Post Opinion