How do I find the messages I have posted?
In the forum specifically?
Go to your profile. Click "Edit" in the "Forum settings" box. The next page will have a "Show posts" link.
Or, click on your username in the header of any post or reply you have written. That takes you to the page with your post count (60) and your 'Show posts' link: https://forum.arduino.cc/index.php?action=profile;area=showposts;u=572977
That shows all 60 posts/replies in reverse chronological order.