My bras never fit

So I always get bras from Anywhere I can get them. I get a bra that’s my size that time and I use the bra, after two weeks the bra doesn’t fit me anymore because I am less than a size up but more of the size of that my bra doesn’t fit me anymore so I can’t go to the store because were busy. So I have to wear the same bra for a month or two until I can get it as a bra. I get another bra from the same place I get them anytime, the same thing happens after a week or two it doesn’t fit anymore. Does this happen to anyone else?

But sometimes it’s also not that bad because then it makes your boobs look bigger

Did I mention I’m only 13. This should not be happening to a 13-year-old