How do you stay motivated to exercise or diet?

I would like to get down to about 150lbs or so but I am having trouble sticking with an exercise plan.
I do good with it for a week or two then I lose motivation and it will take like a month for me to get back on tract.
So any tips or tricks, for dieting or motivation to exercise?

How do you stay motivated to exercise regularly?

Sometimes I slack on real exercise for weeks, especially when I’m stressed from work like these past couple of weeks. At other times I really enjoy my exercise, I usually go running and swimming. What are some things you do to stay motivated?

How can I be motivated to exercise despite depression?

I have depression, and I find that as much as I want to exercise and lose weight, I am having a difficult time getting motivated due to my depression. Exercise does help me feel better and help with my depression, but does anyone have any tips on getting motivated in the beginning and continuing an exercise routine even when feeling discouraged?

How do you exercise and what keeps you motivated?

What would you like to share regarding your exercise routine? Describe and discuss what you do and how it affects you not only physically but mentally and emotionally; the challenges you face in beginning or maintaining the routine; or advice for getting started on an exercise routine. FYI: Im skinny and lazy.