I am 17 years old and my breasts are very saggy. What can i do to fix this?

I am sorry to hear about your concerns. Yes, significant weight gain/loss can be responsible for significant changes in breast size and position ( breast ptosis). If your breast size/shape/positioning are of significant concern to you, I would suggest that you seek consultation with well experienced qualified plastic surgeons once you have reached physical maturity.  You may find the attached link, dedicated to breast lifting concerns, helpful to you as you learn more. Best wishes.

Thank you for your question.  Your experience is quite common for after significant weight loss the breast can droop.  You're still very young and your breast gland it may grow more and improve the appearance of your breast.  I would wait until you're 21 before considering any type of intervention.  If after full maturity your breasts still sag a breast lift may be necessary, I am unaware of any nonsurgical method to actually lift the breast effectively.

Thanks for your question.  A significant weight gain/loss can chance the appereance of your beasts, remember that you have 17 and your body stll changing. I recommend to wait until two years more to see if they can get fully enough and if a that time you feel the same  with no chances, I would suggest to visit a plastic board surgeon in your área. Best wishes!!!