I get lost trying to remember which topics I posted inn....... I'm sure there have been some posts that people wanted me to answer to and I completely forgot which section they were in :/

or is there something like that and I just haven't found it?

Go to the User CP and view your subscribed threads.

Every time you post somewhere you want to know what is going on and remember which thread. Click on thread tools and subscribe to that thread. That way, when you click on UserCP... it will show you a list of the threads you subscribed to and you can always be able to go back and answer again if you wish. If you don't subscribe, it won't show up on your usercp page.

This used to happen to me as well. As everyone stated you can subscribe to threads. You can also automatically subscribe to a thread that you post in by setting the option under your Control Panel -> Edit Options and select the 'Default Thread Subscription Mode' option:

Default Thread Subscription Mode
When you post a new thread, or reply to a topic, you can choose to automatically add that thread to your list of subscribed threads (http://www.addforums.com/forums/subscription.php), with the option to receive email notification of new replies to that thread. Do not subscribe No email notification Instant email notification Daily email notification Weekly email notification

Also - and this does not require subscription - you can remember just one thread you posted in, go to that thread, find your post and click your own name. A frame should pop up that includes a "Find all posts by {your nick}" option. Click that, and you should get an overview of all your previous posts, not just those in the threads you subscribed to.