I would reccomend switching up your exercise routine if you are walking you may want to try an elliptical etc. If your body gets used to the same routine it knows what to expect. If you change up your exercise it will be confused and be forced out of the plateau. And, as others have recommended, if you can fit in a few more mins. a day that may also do the trick.
Good Luck and keep us posted, this too shall pass. You are doing great, and are truely an inspiration to me.
Lisa