this happened to me once. every time you refresh, it gets exponentially larger. an easy way to fix it is to
1: on the bar on top of your screen, click safari > settings.
2: in advanced, click "show develop menu in menu bar"
3: back on the menu bar, click on "develop"
4: click "empty caches"
this may cause websites you visit a lot to slow down for a tiny bit, but i will fix the issue.
- mac addict