Hi Merrikay! I'm sorry about the lost work. You may have logged into the wrong account, possibly by using single sign on while signed into a different email account. I suggest that you make sure you've checked any and all Lucidchart accounts that might be under your email address(es). Your documents might also be hiding in your browser history. If you carefully look through your browser history when you last worked on the document, you might be able to find it. Simply click on the name of the document in your history and it should be restored to your account.
Please let me know if these steps do not retrieve your work!