"other" storage on Mac

I have the Macbook air with 128GB of storage, but about 75 GBs are assigned to "other". This doesn't make sense and I've used OnYx to delete some of the cache but it still hardly makes a dent. I have gone through and deleted all unused apps, unneeded documents and files, which helps me save space, but does nothing to attack this "other" category that's taking up nearly 4 times the next category(Apps at 20GB). Please help.