I think it's hard to stay motivated to lose weight simply because weight is the side effect - the outcome - not the action. Weight loss is passive.
I can stay motivated to go for a walk everyday and enjoy the sunshine.
I can stay motivated to experiment with healthy recipes and find out how pretty and nutritious my meals turn out.
I can work on a personal challenge to complete a set of weights, or pushups, or squats, and beat my previous numbers.
I can throw out all the cereal, potato chips and cupcakes and replace them with oatmeal, salads and apples.
These are things I can do. My motivation is in the joy these actions give me. And, as a nice bonus, if I do them, I lose weight.