Sounds like you have unlocked all items from common-rare. So all you have left are Ultra Rare-Mythic. if you don't mind me asking what is your total MP play time? I've played just over 1 day and only have commons complete.
Made your first hot drop into HaloWaypoint.com
Halo 5: Guardians MP Beta participant.
View your Service Record on the web.
Become a member of an active Spartan Company.