I was planning going to a bar drink some beer while listening to some live blues tonight, but gave up. Getting really tired after work lately, I'm here typing this in my bed and wondering what is wrong with my body.

Do you have a workout/fitness routine? I've always found that helps motivate me to do things like eat right and sleep well

Do you have a lot of stress at work with long hours and maybe even work on weekends? Do you have little to none rest from the stress? Is this maybe going on for a while now?
If the answer is yes, you might be showing first signs of a burnout or something similar stress-related and you should consider seeing a doctor about it. Happened to me not long ago and I had similar symptoms (among other signs).

Do you get enough sleep?