It looks like a couple people have already got forts already up and gathering, which is another caveat.
Uh... We're at turn 13. The game has started more than a year ago.
You should have a fort already up (or two being built). There may be a few exceptions (if you choose a "bad" nation, or if you're really capital centered for unit production), but with our nation knowledge ...
I know, and I believe I've already harped on my own weakness in this thread quite enough; no one's interested in hearing me chatter on about how I'm stuck at -15% income for the
nth time. I just mention it as a caveat because, while I'm not certain about you, I can't tell the difference between a capital fort and a non-capital fort at a glance.
That said, I only spotted five nations with active or apparent construction work being done on secondary forts this turn. That's obviously not exhaustive, though.
EDIT:
I do not have a second fort, and that's because my expansion has been horrible on the island. I am next to two thrones with forces that I could not take without crippling losses, and my start position had a special lamia province next to it. So 50% of the provinces I was next to were not available for expansion, and the rest of the provinces were not connected. One of which was a dead-end expansion-wise, too. It's not that my nation is bad at expanding, or weak otherwise, but the circumstances have forced my hand. I think I have caught up now, but still.
Yeah, you got stuck in an awful corner. I think you could still pull out, but it's going to take quite a bit more finesse than, say, Agor or Illen would need.
EDIT 2: Deadline in three hours, and nation 2 has not submitted. Requesting an extension.