I definitely agree with the nutrition and exercise advice. While you do mention having something of an exercise routine, choosing the bathroom farther away rather than right by your desk is not the same as 15 minutes of cardio workout. I know this well, as I've tried both sorts of workout routines. (Going to the bathroom on the first floor when you're on the fourth, and using the stairs to and from, is closer to the cardio.)
You don't mention temperature at all, or the level of stress from your commute or the social interactions of work. Each of these could play a part in this.
When I was first on my own, living in Texas (I'd been living significantly north of the Mason-Dixon line before that), I found I ended every work day by coming home and collapsing on the bed for a few hours. Even when I didn't have a stressful day at work or a rough commute, once I got home, it was like my energy just vanished. It turned out it was the Texas heat.
- While I didn't consciously notice it being a problem, I needed to turn the AC down a few degrees to be able to be active after work. This was something I adapted to over time, to an extent, but the AC setting is something that can be quick to change.
People frequently discount just how much driving can wear one down. It's an easy task, only requiring a small portion of your attention, it's not physically grueling, it's easy, right? Maybe you're already beating the commute by the times you're going to work and getting home from work. But my personal experience is that the energy drain from commuting, per minute of driving, is peak shortly before the roads are so clogged from traffic they start slowing down. There's hundreds of other cars on the road around me at that time, and I feel I need to keep track of most of them. This fatigue went way up when I moved to Boston, with its much less regular traffic than Texas.
- It's possible that shifting your commuting slightly earlier, so there's even less traffic on the road, would be helpful.
- Public transportation can also be a big help. Sure, it takes longer, but you're not the one driving. Get a seat and relax.
Social fatigue is a real concern for people on the autism spectrum, but there are also others who are affected by it as well. I think just about any introverts will have some fatigue from this, and even extroverts can feel it a bit when they're in a new environment. This does tend to get less the more you know the people around you, but if this is a problem for you, there's other things you can do to help lessen the impact in the short term as well.
- When I was going into the office, I found it to be a big help to spend the last 15 minutes or so with my office door closed, by myself, just recovering from having dealt with my coworkers (not that they're a problem, but I'm an introvert on the spectrum, so socializing is rough for me.)
- I've talked to others without an office door who found hiding out in a bathroom stall or just sitting in their car (assuming it wasn't too hot inside their car) before actually starting out had much the same effect.
- If there's somewhere calm and relaxing near where you work, you could also take a bit of a stress break there.
Basically, the idea on this point is to drop the stress from working before you pick up the stress from commuting. I do realize it's kind of at odds with your getting away before rush hour, but life is a balancing act, and I don't have answers, I just have a list of things to possibly try.