If you have been doing a plan for any lengthy of time it is easy to get into a rut and your body gets used to what you are putting in it. You need to keep challenging your body by really mixing things up. Different HEs, different foods, different meals - really make an effort to introduce a lot of variety into your diet. It will keep the interest up and the weight coming off. After all an athlete wouldn't follow the same training programme day in day out. They are always switching things around to keep challenging their body.
Do you have a food diary in the SW section? If not that would be the first place to start. Have you become complacent? Perhaps not having your superfree or guesstimating your HEs? Not counting all your syns?
And success express and fast forwards are also useful plans if things have really ground to a halt.