As others have said, the closer you are to goal weight, the harder it gets. Your body burns fewer calories as it gets lighter. This makes it harder to create a big caloric deficit, and so weight loss levels slow. Leptin levels change, too; leptin not only controls hunger, but is involved in all sorts of other processes at the cellular level that affect the body's willingness to surrender fat.
The human body is amazing in many ways, but one of the most amazing is how it has built-in mechanisms that evolved to allow humans to survive biologically (where that means reproduction) in periods of famine. Thing is, our bodies didn't evolve to know the difference between a famine caused by a drought or other natural decline in the availability of food, and a famine caused by a desire to look better in a swimsuit.
The good news is that the laws of thermodynamics don't change. If you are burning more calories than you are taking in, eventually your body will let go of fat stores. Unfortunately it will catabolize muscle tissue as well, which is why weight training is especially beneficial for dieters who are relatively lean to begin with. (Obese people lose muscle tissue as well, but proportionately less, and some of the muscle they lose is just the "extra" their body developed in order to help move the excess fat.)
Sorry for the mini-lecture. As you can tell, I find the physiology behind dieting absolutely fascinating. More fun that dieting itself, for sure.
//b. strong
