I just found my old flat female shoes and tried them on. They are a size 13US shoes and they are too big. So now I am confused more as my feet slip out of them when I tried to walk around in them

how the heck did that happen. I am still the same weight as I was 3 years ago?? I normally only wear my runners which are unisex converse shoes (bright red) and they are so old I have no clue of their size...