Loose flabby skin on stomach and deep stretch marks?

Hi, I'm 21 and have two children. An almost 3yr old and a 3mo old. I have horrible stretch marks and loose saggy skin all over my stomach. I used to be in great shape, I was very athletic in high school. But after my first (I had gestational diabetes) I couldn't ever seem to lose my flabby stomach. I went from 107lb to 168lb. Now after having a second child it's even worse. I can't afford any kind of surgery... Is there anything I can do to get rid of this excess skin and horrible stretch marks?

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