Dealing with Plateaus

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I have been on MFP for the last 4 months and have had great success but now I am stalling out with my weight loss. From the beginning I have really gotten into my log, exercising and watching my calories. It seems like for the last 3 weeks I have been around the same weight and haven't made much progress. I am committed to MFP and want to lose about 15 more pounds from the 256 that I have already lost. Should I consider keeping my calorie count even less than what is allocated according to my plan?