Keep it up, keep it up, shelliam!!! Fifty pounds is one heck of an accomplishment!
Plateaus are common for many people following all sorts of weight loss programs. For those of us who lose larger amounts of weight, I think the body needs to adjust every so often and get used to the difference (or something like that).
Strive not to stress out over it (stress can hinder weight loss!). When I can shift my thinking and have in mind that my objective is to become more healthy, rather than simply to lose weight, I do a lot better.