Figured it out. Avast software is hogging ALL that space. It hasn't even finished calculating how much does it weight and it's already at 70GB. I still want to know what could have caused this.
Yeah, WinDirStat is great, I second this. I used this to help one of my friends figure out what was taking up so much space on his computer, turns out it was Space Engineers save files lol.
Avast itself is malware, and it's impossible to remove. I recommend Malwarebytes or just a good hosts file. Windows Defender is great on its own as well.