On google, only my main page (ActiveSleep) and my privacy policy/disclaimer page (here) are indexed. Why is this? My site's only been up properly for 20 days but still...
This is a wild guess here but some of your pages have nothing to do with your site topic. Take the Games page - you have the site title using the Insomnia description yet this page has nothing to do with insomnia. The same goes with the Video page as well. Create a HTML sitemap and have the link on each page to the Sitemap page, this will help the bots to crawl everypage. If you are going to have a site about Insomnia then make sure your pages are about nothing else or at least related to Insomnia. You also have links to UK Credit Cards - UK Broadband - Poker Sites. Again these are off topic and are a perfect reason why Google wouldnt index this site. Keep your outgoing links relevant to your site topic. Although this might not be the actually reason having the site the way you do isnt going to help you in the Search Engines. I would really consider changing your whole site until it is 100% relevant to your topic.
If we submitted a sitemap to google.com/webmaster is there any gurantee all pages will be indexed or not?
no guarantees. Google is not going to give away control over their index. They do give us tools to help them find out more about us (and vice versa).
Guarantee, no one can provide you, however it is highly probable. Try and get as many backlinks as possible, so Google will index you more frequently.
google does not index all pages when you make your web site . it nneds time . make a sitemap . it will help you so much and find more links for your site