There should be an option in your user settings that controls whether or not you automatically 'watch' a thread that you've replied in. There's also an option below the post editor (if you're not using quick reply, or hit the 'more options' button from quick reply).
If you're looking at the 'watched threads' page, there's a button at the bottom of the list to see ALL watched threads, not just the ones with new posts.
And if you hover over your name on the top right of every screen, there's a little dropdown menu with a button for "Your Content" that brings up all of your posts.