Automatic Site Map

I have about 3 sitemaps submitted to google webmaster tools but i have added so much content since submitting them and i don't want to add another. So I need a sitemap system set up so where each time i add new content, the sitemap automatically adds the content to google webmaster tools as well inside the sitemap. I really just want one big sitemap instead of 3 if possible that automatically uploaded content to itsself and google webmaster each time I add new content to my site NEW FREELANCERS ARE WELCOME! If you can do this for free or no charge, there will be more paying work in the future