Contrary to what fitness magazines have you believe, a “high metabolism” is not necessarily a good thing. Metabolism is the process by which chemical reactions take place and cells turn over (degrade and reproduce). An above normal metabolism is a fever.
What you’re looking to do is free up nervous energy. If food is the “gas in your tank”, then your nervous system is the car battery. Its potential needs to be regenerated for you to feel energetic.
One of the most energy-intensive processes we do is digest food. You might not feel this all the time, but if you’ve ever felt sleepy after a meal, then you know how much energy digestion takes. Certain foods/meals are harder/take longer to digest than others. Foods that are of animal origin, cooked, or otherwise heavily processed are much harder to digest than raw foods of plant origin.
Also, not thoroughly chewing, eating too much, too fast, in improper combinations, or in a negative emotional state can stress the digestive process even further.
So stop stressing your body with the foods that you eat.
The second true way to gain energy is not from caffeine, but through rest and sleep. You cannot sleep too much; if you are able to fall asleep, then sleep is what you needed. Notice animals in the wild or even your house pets: they are either very lazy or sleep most of the day, getting up only to explore the world (even if that world is a zoo).
Exercise makes you tired initially, but improving fitness increases your available energy.