It's a pretty common problem for those who stray and stop eating according to SB principles. It really only "works" best as a full lifestyle change. Once you go back to off plan eating to any extent, the weight will come back so it's not really a program you can go off of and continue to maintain or lose. So time to get back on and stay on!
Really though this is why the success rate for "diets" is so very low. It's not that people can't lose weight. People lose weight in all sorts of way. The real goal is to find a way of eating that is sustainable and satisfying enough that you can just keep eating that way so you don't gain it back. "Success" at any level is often mentally an issue if you feel like that you have been deprived and therefore you start feeling like you can afford to eat things that aren't supporting your long term goals and weight management and so you start straying more and more.
????: South Beach Diet Forums http://www.southbeachdietbulletinboard.com/introduction-forum-just-say-hello/5869-getting-back-track.html
If it's just a belly issue then maybe it is just more refined carbs and refined foods in your diet that is bringing back insulin resistance issues and adding the belly fat first even though overall you may not be gaining much.