You're young & so pretty, I'm sure you'll look cute no matter the clothes.
Like others, I also recommend thrift stores or Goodwill if available where you live, or garage sales. Sometimes you have to kiss a lot of frogs to find a prince, but it's so rewarding! Great if you're able to get something cute & cheap, and then be able to re-donate it a few months later when it's too big!
I'm a lot older but in the same boat, don't want to buy clothes now but have a reunion coming up so have to have something to wear. My body better not think this is the new weight just because I'm buying something to fit it!!
Good luck!