Memory Usage Problem With iPhone?

I have a tethered jailbroken iPhone 4(GSM 2012), i only have 3 apps from the app store downloaded, and a few more from cydia, yet my iphone says i've used up around 6.1gb out of the 8gb i have, i can't download any apps cause of this, yet i also don't know what's taking up the space, is it the cydia sources?

Cydia it self use a LOT OF SPACE mine uses 2.7 GB you should download icleaner from cydia it will clean up somespace.

EDIT: and if you have a iphone 4 that has 8 GB. Then that explains everything cuz I have iphone 4 8 GB and it has 6.1gb space (the other 1.9gb is used by the system)