I wish I had something comforting to say here, but I gotta admit that this is the case for me as well. Ten years in the working world, and I am still mentally (and a bit physically) tired after an 8-12 hour day at the office. I don't want to do anything after work. Two years ago I volunteered on a political campaign, and the evening meetings during the workweek were exhausting because I was already wiped from work. I tried to do as much on the weekend as I could, but most volunteer groups meet during the workweek.

In all likelihood, you will adjust after a while and be able to do some stuff after work but I honestly think you can't expect yourself to be able to do all that you did before either.