Aw I get that Ally 😭 I did the same thing last year lol. I just make sure the clothes I buy are a little stretchy (especially tight fitting stuff) so that I I gain/loose some they still fit.
I got nearly all my formal dresses off club london. I've some really nice dresses, although they can be a bit pricy (I'll wear them again so doesn't matter too much to me lol)