When you click on "Your Houzz" a drop down menu appears. At the very top of the drop down, click "Your Houzz" once more (right beside your profile pic) and this will take you to your page. You should then see 3-4 choices (tabs) just above the photos for your Ideabooks, and one of those tabs should say xx Posts (xx meaning the number of posts you have done, which show your Discussion participation)
your Design Dilemma should be listed there.

If you aren't getting any E-mail notifications that someone has commented on a discussion you started, then check your privacy settings, or send an e-mail to support@ houzz.com, as they are very helpful!