Site not displaying new posts until manually refreshed

I’m hearing from a bunch of readers (and seeing myself) that my site at joelsgulch.com isn’t displaying new content unless it is force-refreshed. This applies to both new posts and new comments. I just upgraded to WP3.5, but the problem began about a week before that, when I was using 3.4.2. I called tech support with my hosting service, and they couldn’t find anything amiss. Any suggestions?

Thanks!