I have two thoughts to share:
What types of classes are you taking? Are you doing weights at all? If so, you may be gaining muscle but losing fat and this could result in a lack of weight loss, but you could be shrinking and shifting your body composition. That would be a good thing. Rather than measure pounds lost, you may do better to measure your body composition and keep track of that.
I lost 65 +/- pounds (depending on the day) over the course of a year and a half and have been keeping it off. In order to maintain, I make myself eat according to the food pyramid. After I have eaten my 5 fruits / veggies, my 2-3 milk products, etc, I still allow myself a treat. The thing is, after I eat all that healthy stuff I don't usually have any room left and end up skipping out on whatever it is I was going to have! Go heavy on your breakfast foods - that first meal can set you up on whether you are hungry all day or satisfied. I usually start out with an omelet made with eggbeaters (or you could use egg whites) and veggies such as mushrooms, broccolli, onions, or peppers. I have either whole grain toast or a whole grain English muffin and top it with reduced fat butter and sugar free jam. Mid-morning have a piece of fruit. Now you've knocked out 2-3 servings of fruit / veggies and you've kept yourself full.
Good luck. It's a lot of work but once you get going with it you'll be fine. You've already taken a good first step by joining a gym and attending some classes.