Dell Backup and Recovery

I hope someone can help me. I have been trying to setup and use DBR. My problem is this, the original backup was to an external USB Drive.  This drive was very quickly filled to capacity. I then selected another external drive, within 2 days this drive is 90% filled. Next I purchased 20Gb of cloud storage it filled in 3 days. Then added an additional 20Gb of cloud storage and this is now filled and my backup has been suspended. At the same time files were  continued to be backed up to the external drive. Now that drive is full.  Can someone tell me how the files are being backed up? Is a new copy of my files being created each time a backup is performed? If this is the case I will never have enough space. Shouldn't be that each backup will overwrite the old files with the new. Is there some setting that I have not set correctly?

Thanks for any advise that you could offer,

alpo007