What part of Canada do you live in ? There are some good clinics in Ontario and some other areas.
I doubt the doctor will agree at all about a chiro. Most doctors are very anti-chiro.

If he is exhausted so easily, he is likely not getting good sleep. He needs quality sleep to heal. Quantity sleep can actually limit quality sleep. I got my best sleep in a recliner with a nice blanket. The recliner helped me keep my head in a good posture. I would get deep sleep and wake up alert. I would do a light activity then nap for a short while then repeat with a light activity.

He needs to get good REM and slow wave sleep. That is where healing happens. Without it, he will feel groggy all day. The brain can only flush toxins during slow wave sleep. It only heals neurons during REM sleep.

As I said, he also needs to stimulate blood flow to the brain without increasing his headache.

With his level of symptoms, I don't think school should even be an issue. The sights and sounds of school are likely far more than he can handle. Maybe the school can send home some light work so he feels like he is moving forward.

He should be free of headaches and not have any foggy brain feeling before he returns to school. He should be able to tolerate TV and doing a school assignment at home before he returns.

Since Sidney Crosby and a few others, Canada has developed a bunch of competing protocols for concussions. The guidelines put out by ParachuteCanada are weak about how to handle your son's current stage. They miss the importance of stimulating brain blood flow with low stress activities and think quantity sleep is appropriate even if it is not quality.
US research shows these to be most important.

One of the issues is that bed sleep during the day disrupts his normal sleep cycle. Quality sleep happens best during his normal sleep cycle at night. A few short naps during the day are OK if they are not restless toss and turn naps.

If you have a hour available, sit and observe him sleep, paying attention to his breathing. His breathing should be regular, not shallow then gasping for air then shallow. Ask him about his dreams when he awakes. If he has any stressful dreams or night mares, take note and tell the doctor. They are often a sign of poor blood flow to the brain or poor oxygen.

A Fit Bit can track his sleep a bit. It will show how much he stirs.

I hope he starts feeling better soon. I know his frustration.

My best to you both.