That seems to happen in every game, doesn't it? This is also the first game in which people who have nothing new to say actually refuse to talk to you. If you walk up to someone and they brush you off, don't take it personally; they just don't have anything new for you.
Here are some things to try if you're dead in the water. -- Talk to everyone about everything and return to all locations to see if something's changed.
-- Go down the task list and see if there's a puzzle you've been avoiding. I once got stuck for quite a long time before I realized I'd never completed the sails quiz in the Culture Center.