2-3GB is a bit tight.
It could be:
- Windows update running in background( they now claim extra 7GB's I believe for updating to go smoothly): check in taskmngr?
- Disk failure: SSD or HDD? did you run a check?
- A virus: did you recently install/download any software / run antivirus check?
*)I must say two weeks ago my D: hard drive suddenly was getting low on space and now has 28GB free again, so that's also rather odd.
When I checked there are now less System Restore points to revert to. Perhaps it was eating up exces space?
Or could be a cloud service, syncing gone bad. Still very odd.