You are what you eat is very true & is the basis of the principle in ancient Indian medicine - Ayurveda.
However even more basic than food as a source of energy & yet the most overlooked is our own breath. About 80-90% of stress can be withdrawn from the system through proper breathing. The quality of our life (life-energy) in this case is directly related to the state of our mind. Through various intensive breathworks like Art of Living Part 1 program, one can easily learn how to have the system maintain a daily surplus of energy at all times. Advantage - you dont need to go anywhere to practice breathwork once you learn how to master it - laziness can creep in to go to the gym or pool or run.
You can find details at www.artoflivingaustin.org

Other techniques that complement breath also are Yoga, Meditation, Satsang (chanting/kirtan in a group setting).

Ultimately the life is in our hands & understanding the principles in which the consciousness functions can have a tremendous boost to the quality of one's life & enrich it.

In addition to the recommendations Jessi gave you. Make sure to observe the quality of your food. Ideally most meals should be organic, hormone free and free range. Or simply eat as little processed foods as possible.
Another overlooked factor is sleep. Try to attain 6-8 quality hours per night. This will help you recover & prep you for long work days, challenging workouts and the summer heat.

George Tabares
Fit. Spec./Asian Bodyworker/RMT

You're right, the food could very well be what's causing your energy deficit. Oftentimes it's as simple as dehydration. That is always the first, and easiest thing to try. The general recommendation is at least 80 oz. of water (just water, not juice, tea, soda, etc.) per day. Lack of hydration can cause weakness, fatigue, water retention, etc. Also, proper timing and combinations of food is important. If you are eating too many or too few carbohydrates or not combining them well with protein, fatigue can set in. Try going no more than 4 hours without eating. Make sure to have a protein source in each meal and consistent amounts of carbohydrate at each meal as well. Good sources of carbohydrate include whole grains and fruit. Protein sources include lean meat, nuts, and low fat dairy. For further help on meal planning, please feel free to email me at the address listed in my profile.