This quote keeps me motivated: Weight loss is about commitment; it's not about motivation. You have to commit to it like you commit to taking a shower or going to work every day.
Motivation comes in waves and if I waited for motivation, I would probably only stick to my plan a few times a year
SO, I remind myself that I am the type of person that remains committed to things whether it's to my family, my job, my friends etc and now my "diet".
Hope that helps.