I also would like to know how to find one's original post. It took me a long time to find mine (<1 day old) as several keyword searches didn't work (at least in the first 50-100 hits).
Clicking on my name and all i get is some crazy circle that does not stop, so that is no help.
After you are logged in to the community
Try clicking on the little icon in the upper-rt corner of the screen that shows the outline of 3 people.
Then select "My Profile" from the dropdown menu.
The next screen (Below the Badges) will show three selections for listing your most recent:
Replies.....Posts...Drafts..