I think it's important to remember, too, that South Beach is not a "quick way to lose weight." It's a lifestyle change that will cause you to lose weight (if you have excess weight to start with), but most weight loss isn't sustainable if you lose more than 1 - 2 pounds per week.
Second, I've read several posts on this forum from people who are starting over on South Beach, and virtually all of them said that they did not experience the same dramatic weight loss during Phase 1 as they did the first time. You're not alone.
Third, when you do lose a lot of weight in Phase 1, it's mostly water weight. When you start adding in some higher glycemic index foods (like fruits and grains) in Phase 2, the water weight-loss is going to slow down.
Fourth, muscle weighs more than fat but takes up less space. (It's kind of like that old joke about "Which weighs more, a pound of feathers or a pound of rocks?" They both weigh the same amount, but it takes a lot more feathers by volume to make one pound.) Since you're doing regular gym workouts now, you're probably burning up quite a lot of fat, and replacing it with muscle. So don't just go by your scale's numbers. While you may not be seeing much weight loss on your scale, are you losing inches? Are your clothes a bit looser than they were before?
Although South Beach is not a calorie (or anything else) counting diet, the truth is that you gain weight when you take in more calories than you burn. You lose weight when you burn more calories than you take in. As long as you're eating in accordance with the South Beach way of eating, and especially if you're working out several times per week, you WILL lose weight. But the human body is a pretty complicated thing and, as a result, weight loss (or gain) isn't always a steady progression. (Have you ever totally "pigged out" on something, and it took a day or so for the weight to show up on the scale? I know I have.
Don't give up. You're off to a great start!!!
And if you want to lose about 50 pounds before your wedding next year, at a sustainable weight loss of 2 pounds per week it should only take you about 25 weeks to lose it all. That should leave you plenty of time for dress fittings on your new slimmer self before the wedding.