I hear you. I am 17 days sober...the first week I was so unbelievably tired. I still feel very tired but it is getting a little better.
I also used to notice that when I drank I had energy, but it was really just fake energy from my nervous system being fried. When I had a night off the booze, the next day I would be asleep all day.
You are "catching up" on a lot of rest that you hadn't been getting when you were drinking.