How do you stay motivated...

To eat healthy & exercise. I am 140 Ibs & want to get down to 120 Ibs, which is what I used to way 6 years ago. I don't have a problem losing weight as long as I eat healthy & exercise. But I can't seem to stay motivated to do either of these things. I'll stick to a diety & exercise for 2 weeks, then get sick of exercising & eventually eat pizza. Does anyone have any tips on staying motivating, or great ideas for losing weight?

Thank you in advance
How do you stay motivated...
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