Working Blues

Is it possible to be this tired after working only three days this year?
I feel like such a wimp. (Does anybody use that word anymore?)
I'm sitting at my computer, waiting for Spencer so I can drop him at school before I go teach -- my fourth workday of 2012. My energy is fine right now, but yesterday evening, I was a limp rag, and grumpy. I expect the same results after I work today.
The thing is, I don't even work regular hours like most people do, which gives me even less reason to be so exhausted.
I do have two days this quarter where I work 8 to 12 then come home for the afternoon and work 6 til 10 p.m. That's what I did Wednesday, which probably added to my tiredness. And I could point out that the evening class is north of the city and I have to leave about 5:15 to get there. Still, when you add up all the hours that I'm physically teaching, it's not much compared to the hours most people work.
My husband, always on my side, would point out that I spend a lot of hours at home preparing for class and grading papers. I can't shake the feeling that if I had to work a regular 9 to 5 job, I'd never make it.
Last night, I knew I had to go to the grocery store. We were out of milk and eggs. Tucker needed snacks for a swim team trip this weekend. I sat on the edge of the couch, ready to pull myself up and go to the store -- for an hour and a half before I finally shoved myself out the door.
I patted myself on the back for having prepared dinner every evening after work, but when I walked in from the grocery store and the sink was still full of dishes while my teenagers lounged around the house, I wanted to scream. Well, I might have done a little yelling.
And the teenagers weren't lounging all day. Two went to school, one went to jury duty. Two had sports practices and one volunteered in the high school costume shop for the upcoming musical. Then they lounged.
The scary thing is that I like my job but I'm still feeling over my head trying to keep up.
How about you? Are you exhausted after work or does it just take some adapting to the new year?