here's life

This morning I rode to work on a bike.  It was fun, speeding through the crisp dawn air.  After work I peddled home again--upwind most of the way, and it seemed like there was more uphill than down.  I take a route that keeps me away from the main roads almost entirely, and only include a little grass.
I heard at lunch that I am supposed to have a bike license.  That it cost $12.  Interesting.  I'll have to look it up and find out if I need brakes and such. (which I have, but they don't meet the "skid on dry pavement" test)  
But, the question is, can I keep it up?  Riding to work means I need to wear pants over my good pants to keep them out of the chain, I get either cold or sweaty on the way to work, I have to carry my lunch in a backpack, and so I can't really take the half gallon of water I am used to drinking everyday.  I also have to get up a half hour earlier.  But, it makes me stay more awake in work, (when combined with enough sleep and the right diet, exercise,,,) and I get some good cardio---although I don't ride at a panting pace like when running. Having been the same route 4 times now, I am starting to get tired of it.  Can I continue to ride this path even when I am tired and don't feel like it?  Should I?  There are so many things that demand my attention, time, energy and motivation, and I am only one person.