Is there a way to find my active posts?
or to see which of the threads I've posted on have responses?

In the upper right side of every page you'll see it say you are logged in as edshern. Click on your name or click on the avatar on the left side. Those will take you to your profile where you click to see your posts in the last 30 days. if you want to see more than 30 days, use the advanced search on the left of the page or the search button the right of the page. Then enter you user name. This will show you all of your posts.

You can be notified of posts made to topics you started by selecting that option when you first make the post. Currently there is no feature to allow you to be notified if you didn't start the topic.

Thank You