My depression makes self worth & motivation a challenge. I try to ignore my negative thoughts. I talk frankly with my 7 yr old about how bad obesity feels and why people need to be healthy - healthy, not skinny. I fake motivation when it's gone. I applaud the tiniest success and forgive my failings.
Tell yourself "I'm a person of change." Make up affirmations, a phrase or a picture. I drew one of me liking myself, at times I write down good things I do. Ask for reminders about water, walking etc. Stop being ashamed about size, fitness etc. be proud of trying to do something about it!