I commuted for years once, twice and three times a week (15 miles) but never all five days until one week I tried it. I was on my knees by Friday but eventually I worked back to a full week and was ok. I find I need my sleep and cannot go without 7-8 hours or I suffer. I needed to eat the right food not just quantity.
Commuting is different from leisure cycling at weekends because you are working in between and even if you feel you do not have a physical difficult job it still takes it toll physically and mentally.
My routine is similar to BoardinBob – tea before I leave then a Muller Rice at work with coffee. Lunch was loaded with carbs and then an afternoon snack about an hour before I leave work such as a banana or muesli bar. And oh yeah, the water intake is important during the day and on the commute.