mine only shows 1 old sent message, possibly my first one sent
Interesting. I don't send messages, but I sent one to myself and confirmed that it did not appear in my sent items.
Found this:
https://www.simplemachines.org/community/index.php?topic=547697.0In short, the forum appears to default to not saving sent messages. You can manually check the box to "Save a copy in my outbox" on individual messages, or you can go to Profile --> Personal Messaging and check the box for "Save a copy of each personal message in my sent items by default" (this setting will automatically check the box mentioned previously). Be sure to click the Change Profile button before navigating away!
Unfortunately, I expect that won't work retroactively, so I'm not sure how you can get your past messages. Contacting the recipients (if you remember them) may be the best option. Maybe one of the mods (or another user) has a better answer!