No luck with that. The next thing that I thought was that it could have been my backups from rooting my device, since I have been searching for the solution to this problem for a rather long time now, I have found out that CWM backups can take up quite a bit of space, but I had all my backups on my external SD card, so that ruled out another possible cause.
Also, I have read on another thread that Google Contacts Sync could take up a lot of space...
After getting slightly discouraged, I resulted to going back to the internet and looking for other possible causes. I read that somehow Google backs up your photos that you take on your device, so I wondered if the backed up photos could have somehow snuck into that "System Data" file. I searched for a while, and finally gave up.
So, the question is, what is taking up all this space, and how do I get rid of it??? Thanks in advance.
Here is a screenshot of my storage followed by DiskUsage: