I was having the same problem, only over a course of months. Starting last fall, I began exercising regularly (4-5 days a week). People started asking if I'd lost weight. No, my scale says I haven't. Go shopping and SURPRISE! I've dropped a size. Continue working out until last week when I got an ear infection. Essentially took the week off, the first time in months. Magically, I lost 3 pounds. I think in my zeal to not "fall off the wagon" regarding exercise, I forgot that occassionally my body needs rest. At any rate, I knew that it didn't really matter what my scale said, I felt great. Don't get discouraged!