This is a server side code and thus the repeater will only refresh when the browser pots back the page or gets the refreshed page again.
For the data to refresh automatically, you either need to poll the server in a defined interval to get the new data. You can do that easily using jQuery and AJAX. Or the other option, which should be used when you need real time updates (example chats, facebook notification), is to use push technology.
SignalR[
^] is a library which helps achieve this very elegantly. Checkout the link and and decide if that's what you need.
Hope that helps!