I think that to follow or not follow a discussion all you have to do is to click the "Follow" or "Following" button in the top right. Clicking it again will toggle whether you are following or not.
To find your questions and discussions, simply login and click your name in the far upper right where it says:
Welcome, ( Log out)
and click your Content tab. You'll see everything you've ever posted or participated in.
You can also search the forums and just enter your name or the topic you were looking for.
Hope that helps!