20 and what to loose weight for big 21

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Hello my name is Bri and I'm 20 yrs old. I need to loose about 25-30 lbs to be at a healthy weight. I've already lost 23 lbs in my last efforts to get fit but this half way mark sucks. I can't seem to get motivated enough and unfortunately I began to eat unhealthy again and that habit is hard to break! I want to get fit by 21 and my birthday is July 12. My family is planning a beach vacation and it would be awesome to celebrate another year and the beginning of living at a healthy weight. Anyone somewhere near the same situation? I would love some motivational help!