It's hard to say what's going on without knowing how you lost the weight previously and what your eating and exercise habits have been like for the past year. If you used to lose weight through starvation diets, these may become less effective over time. However, if you are consistently exercising, and are moderately controlling your calories to lose weight and you don't see any change in the scale, you may want to consult with your MD to rule out any thyroid issues.