This is what i know... u only signed in to iCloud and it increased to 1.7gb ? Or can u recall doing anything else?
Basically, anything stored on your iDevice that cannot fit into one of those 8 categories is categorized as "Other." This includes:
Browser cache
Mail cache
Mail messages
Mail attachments
Safari's Reading List
iTunes Backups
Crud resulting from jailbreaking your iDevice
Game data
Saved data files
Call history
Notes
Media
Voice memos