I did an interview with the NY Post last week re: Kate Middleton's weight. I was asked if I thought the bride to be looked too thin and I said she looked fine. And no I don't think she'll become bulimic like her late mother in law.
Some people don't eat when they're stressed and others do. Depending on how you manage stress you may lose or gain a little weight before your wedding.
Some brides put together a fitness plan to get in shape and that's fine as long as it's a healthy plan and that you don't over do it. You still want to look like yourself on your wedding day, not a rail-thin version of yourself.
If you don't already go to a gym you may want to take some of your wedding budget and put it toward aerobic or cardio classes or sessions with a trainer who can help you tone the areas you want toned and give you general advice on what you should and shouldn't eat.
As for Kate's weight, like any bride I'm sure she wants to look and feel beautiful on her wedding day and the added stress of the entire world watching isn't making the wedding planning process as much fun as she thought it would be.
If I was getting married today I'd follow her lead: exercise and eat healthy, and ignore ugly comments from people who are probably jealous of your happiness.