When you need a reason to get back on track, stay motivated, whatever... Look back. Look back to when you first started your journey. How did you feel? What did you want? How does that compare to now? What have you learned since then? Too often we forget what we've accomplished and let negative thoughts into our lives.
It's easiest to look back if you keep a journal! Try writing in one at least once a week with your feelings, and both good AND bad things that have been happening.
For one (of many) examples on looking back, check this blog out: http://www.sparkpeople.com/m