I used to have that problem too. People were telling me "congratulations!" all the time. I hated it.
Some CFers call this belly a "kangaroo pouch" which I think is a nice name for something that makes many of us feel so uncomfortable. Not every CFer has a kangaroo pouch, but many of us do. Cystic fibrosis patients, because of the problems with their bile ducts (I'll spare you the technical details) tend to have some degree of liver damage. Long story short, what ends up happening is that we get extra deposits of tissue in our abdomen. If you'd like to read an article I wrote about cirrhosis, it explains in greater detail why the kangaroo pouch occurs.
Before I switched to a different type of pancreatic enzyme supplement, I ALWAYS had a kangaroo pouch. Now my tummy, although hardly washboard flat, isn't so noticeable.
There's only so much you can do to get the pouch to disappear. Weight loss isn't a safe option, but changing the diet is. Try to stick with foods that don't have as much potential to make you gassy or bloated. Stay well hydrated too, which helps your liver stay in balance with the rest of what goes on in the abdomen.
I tend to camouflage my kangaroo pouch by wearing blouses that are loose at the bottom, and more fitted at the top. Unfortunately, the trend right now for women is long t-shirts, which aren't always flattering to the CF physique.
It took me awhile to learn not to be self-conscious about it. A few laps around the mall and I realized that people with FAR nastier bellies than mine were squeezing themselves into clothes that were quite unflattering. As long as you dress for your body type, you should do fine.
Oh, and elastic waistband pants are a God-send <img src="i/expressions/face-icon-small-smile.gif" border="0">