I did not feel better from the nausea and exhaustion until 30 weeks or so, and by then all that happened was that my HG/nausea dissipated was replaced with sciatica and constant acid reflux that made it impossible for me to lay all the way down.
Some people just have miserable pregnancies. I remember being told frequently "oh it gets better in the second trimester" while I was IN the second trimester. Every pregnancy is different.