Around 22 weeks was when I finally had energy back..and then it was gone again around 33-34 weeks. I think that happens to prepare you for the sleepless nights early on.
I had only a very brief reprieve from it - mine didn't let up until 17w, and returned w/a vengeance at 27w. Chasing 24 kindergartners all day though will do that to you.
The second trimester is definately the time to get things done, the first and third are so tiresome and at the end you are just so uncomfortable when you have any energy its hard to to anything.
Re: Tiredness
... every single day of forever.