Will Google automatically re-crawl a sitemap?

[steakaphagus]

Hi, in Google 'webmaster tools', I've submitted my site's sitemap - each time I've added pages to the site, I re-submit the sitemap, but have noticed that this seems to 'reset' my site's info on Google, such as external links etc.
Am I not meant to resubmit my sitemap every time new pages are added? Will G just eventually crawl a new map?
Thanks

[maximillianos]

You only need to submit it once. They will periodically check it for additions.

[steakaphagus]

Thank you!