Are you 110% sure that you have entered the correct 4 keys for the Twitter API? If db/cache/lifestream.php is almost empty, the call to Twitter has failed (because of wrong keys).
A general piece of advice. The extension is caching data for 10 minutes. (All Twitter data is cached in the file db/cache/lifestream.php) If you change the Twitter configuration (for example Twitter search term), it might take some minutes before the new results appears unless you manually delete db/cache/lifestream.php. There is no need to delete the file, if it is "empty". In those situation, the extension will always try to download new data.