To my knowledge, there's no record-keeping system on these forums that keeps track of your recent topics and/or posts. However, if it's a relatively recent topic/post, you should be able to find it in the first few pages of the forums; the boards don't move terribly quickly, so it's not too much of a chore to find something current. If you don't remember what it was, then it probably wasn't worth going back to anyway. :P

Failing that, if you remember what the topic was about, you could always just do a search for key terms using that search field up in the upper-right corner. Or a quote that you remember seeing.