Recent Obsession

So, I am obsessing of late over my stomach.  Aside from the fact that I have slimmed down in almost every other area, my belly has been getting bigger over the past few months.  I can't see how this has happened! What has changed?  My diet is a little better - although I have moments when I am completely naughty... and ok, so those "moments" sometimes last a couple of weeks.  But I always get back on the wagon.  Kind of a depressing thought, but I'm 31 next month.  All those things that I've heard from others time and time again... "when you turn 30 your body turns on you" and ya-da ya-da ya-da.  So what, I have cholesterol like a stag, I am fit and frankly, it's amazing how I pull off weighing as much as I do.  Muscle?  I doubt it.  It's this damn belly.