Whenever I click it on my profile to find one of my old topics or posts to very hard questions with answers because I forgot how to do something, the site only finds a few of my topics or posts, not all.

Click on your username (in a post) to view your profile. Then click the "Find my content" button.

Alternatively, you can use the advanced search:

http://www.msfn.org/board/index.php?app=core&module=search&search_in=forums

Which is the gear to the right of the search box. There you can search by username, etc.