If you put your mouse over your name in the upper corner a pop up box will come up and there will be a little link that says show all post by me. Click on that and your post will show up. It only works in some communities though.

You can use this code also in the browser.

http://community.livejournal.com/COMMUNITY NAME/?poster=YOURNAME

Just put the community name and your user name where the uppercase words are.