Originally Posted by GrainBrain

What's your height and weight? Are you consuming enough food throughout the week - trying eating some more proteins and fats. Sugary carb focused diet could be a problem. I get my vegetables by cheating and buying the steamer bags, often with the sauce. Complex carbs are the key to good health.

You didn't mention what you eat after riding? This along with your need to nap makes me think you're just hangry. Immediately after you dismount consume something with fat, protein and a little sugar, I like a cup of chocolate milk. Eat eat eat. A cold sandwich is great and takes a minute to make. PB&J is awesome as well.