1- Click on your user name at the top right of the screen. A popup will be displayed. There is a link in that popup saying "Your content". If you click on this link, then you will see your threads and posts. It basically makes the search for you quickly.
2- At the top left of the screen, there is another menu item called "Find threads" that you can also use to get your content:
This second one could be hidden if you scrolled down the page. Then you can access the same menu by clicking on the drop down button on the Forums main menu item. And you get the same "Find threads" and sub links.
Second option might be much better, because it is grouped as shown below. You can access the threads you started, threads you contributed by posting, and your watched threads.
This is a whole new software that we recently migrated, and we are also having some difficulties to find different things that we were used to find easily in the old software from time to time, and trying to adjust the settings for best user friendly experience. Please let us know if there are other things that you are having trouble to find out.