I can say that there is definitely nothing wrong with you. I went
through something similar. I first knew Iwas pregnant because I was
falling alseep (literally) at work, and that is pretty much how my
entire first trimester went. Then trimester 2 arrived and I felt much
better. Then around week 26 I just lost all energy and had morning
sickness again! I could not make it through my work day, and I was
feeling like such a wimp because you hear of women who lwork until the
day their baby is born. Well I had a lot of pressure from my boss to
continue working at full capacity, so I just kept trying and pushing
myself until I just broke down. It was not pretty. I had to force
myself to cool it and also be firm with my boss, neither of which were
easy.
I also wondered what was wrong with me, but my midwife assured me that
some women have a third trimester very similar to their first and it
was totally normal. There is nothing wrong with you!! Just remember
that every woman has a different experience with pregnancy. Just be
sure to listen to your body and if you feel tired, lay down! Don't
push yourself!

Best Wishes and good luck!