Based on your question, I'm assuming you have added your site inside Google Webmasters Tools, right? Unless you see any errors in the XML sitemaps section of the webmaster tools (it's under the "optimizations" section) you don't need to resubmit, the google spiders will crawl it with certain frequency and update the information.
You may set the frequency of each and every link in your sitemap. The xml tag is <changefreq>. Values to this tag are always,hourly,daily,weekly,monthly,yearly and never.
It is fine if you have submitted only once. Google will crawl it and update the information. It may take some time.
Just update and submit your XML sitemap when significant changes to your website has occurred (e.g. you have added new pages to your website)
Google will automatically check your sitemap and the frequency will change in response to how often you actually post. As for updating the actual sitemap - it's generated by a script, right? You shouldn't have to do anything!
Google crawls your sitemap periodically, according to some factors they use for the frequency. You do not need to resubmit.
I think, it depend how many pages you creating weekly or monthly. you can submit your sitemap whenever you create new page like 50, 100, its all depend upon you. if you creating only 6-7 pages it is better to go google webmaster tool and use fetch as Google. it will help for indexing page in Google. May be this help you.