I have had moments where I question my ability to continue this journey. What I find that helps me, is to pick something up that is the equivalent of the amount of weight I've lost. This way, I know that I have come a long way, re-energizes my motivation to keep going.
Another thing that may help is to sit down and put a list together of your previously met goals, and the postive outcomes of your lifestyle change. If you ever question the benefit of your lifestyle change, a posted list of benefits on your refrigerator will put it in plain sight!