Are you eating breakfast? If not, then you're starting on empty and always trying to catch up.
My commute is 29 miles RT. I always eat something at home and like to eat again after arriving at work. I believe this helps me through the day and the ride home.
In the morning, hot cereal and/or fruit. In the first 30 minutes at work; yogurt or fruit, even peanut butter and jam. I prefer to eat real food on commute days, no bars or gels.