Might be what you eat.
I, too, struggled with energy during the day. Not only do I work shifts, but I travel internationally a lot and jet-lag is much like shift work.
It sounds like you are doing everything right as far as keeping up your exercise. Good on ya! I'm in the same age range and I've recently changed my diet to lose weight but discovered that it had a really nice benefit of equalizing my energy level all day.
My wife and I read "The Four Hour Body" by Timothy Ferriss and I adapted my eating style to the way he suggest in the book. In short: for 6 days a week no carbohydrates or sugar. From Friday through Wednesday (the weekend is Thursday-Friday in this part of the world) I don't eat:
- White food (if it's white, it's probably full of sugar or simple starches)
- Fruit or fruit juice
- Bread
- Rice
- Pasta
- Anything made from wheat
- Grains
- Sweets
- Potatos & Potato products
- Sodas and sugary soft drings (Get rid of that anyway)
- Anything deep-fried
It sounds like one of those privation diets that people hate but the key for staying on it is the "eat trash day." On Thursdays, I eat whatever I want. in fact, I make it a point to eat the bad-for-me food. I have Cinnabon for breakfast, pizza for lunch, I'll go through several cans of Pringles (dear lord those are like crack!) and eat M&Ms like I was Pac-man!
I still eat well. Lots of vegetables and protein. I often replaced rice in dishes with lentils and found it a lot more rich and tasty I also don't have to worry about eating too much fat (as long as it's the good fat) and never feel unsatisfied. If I crave a can of Pringles on a Saturday, it's easier to resist because I tell myself I'm saving that indulgence until Thursday. I strongly suggest reading the book and basing your eating habits on that rather than my abbreviated description here. There are many other tips like always eating a high-protein breakfast within 30 minutes of waking up. That REALLY works. On the days I don't do that, I feel like I'm a step or two out of rhythm.
I did the diet as a series of small changes and discovered, after 4 months, that I had lost almost 35lbs (That's about 8% of my body weight) and my fat content in my body dropped from 30.1% to 19% (and continues to drop). I continue to eat this way because the biggest benefit is my energy level.
I get tired at the end of a day, sure but what I don't get is tired after lunch, Tired after I wake up, tired in the middle of the day. It's as if, once I get the "motor" running (with a few cups of coffee) It runs like a well-tuned 360 V-8 AMC engine all day and when it's bedtime: BAM! Asleep.
Exercise is key and is a really useful tool for regulating sleep. I almost always work out after a night shift. It may not be a full-on crossfit workout or massive weightlifting session. In fact, often the best way to get ready for bed is a 20-30 minute brisk walk. Clears out all the remaining catecholamines in the blood from the shift before and makes it easier to physically relax. I used to work with a guy who was former Airborne and he's get on the treadmill and do a brisk 2km before bed each night. He'd knock out like a light and I've never seen him tired.
Good luck and good on ya for taking care of yourself.
--maddog