There are tabs just above the discussions that have been started, one of them says "My Discussions". If you click on that, it will take you to every discussion you have read, commented or started.
An easier way to do this is to click the heart next to the thread title while you're in the post. This marks it as a favorite and can be found in the "Favorite Discussions" tab.
Also, if you look under the category list (the one that you can expand and collapse) you'll see a forum search box. I haven't used it yet, but if you type in your user name you should be able to pull up everything you've started.