Question: Startup disk almost full message
I am getting a startup disk almost full message on my Mac. When I check the storage, it shows almost every single GB being used in the system section. I have deleted all of my pictures and everything extra and it freed up about 1 GB, but then the space went back down to only 8 MB available. This started happening a couple days ago, not long after the new system update. I have tried the clean my Mac, but it did not help. I have also tried starting my computer in safe mode, but it shows the same information. My battery has started dying a lot quicker now than it did before and is running very slowly. What can I do to fix this? I have only had this computer for about 6 months.
MacBook Air, macOS High Sierra (10.13.3)