Time Machine backs up a huge quantity of data on every run
Take a look at BackupLoupe:
http://www.soma-zone.com/BackupLoupe/
The blurb on the website describes what it can do far more eloquently than I can, but to summarise it's commercial software that you can evaluate for free and then pay for if you with to use it. Once you have determined which backup intervals or which files are taking up more space than you wish, you can delete files across all backups or delete snapshots as needed to maintain storage space per your requirements and preference.