How can I shed last stubborn pounds?

Hello! I'm 15, and started a few weeks ago with a weight of 127 pounds. I'm 5'9", and hoping to get down to 115. I have a very small chest which does make my weight lower, I'm not underweight or anorexic! Anyways, I've lost 7 pounds, and currently weigh 120, but those last 5 pounds will not go away! I'm on a 1200 calorie diet, with once weekly gym visits (I can't go more often, so it's not an option). I skip breakfast for convienience reasons, eat a large lunch, and small dinner or replace dinner with an afternoon snack. My lunch is made by the school and it's usually quite healthy, some kind of roasted protein/fish/pasta with salad, or I just have a salad and yogurt.

How can I lose these pounds? Thank you!
How can I shed last stubborn pounds?
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