Thanks for posting this thread, we are just getting started with considering the same thing.
For the past 7 years my son has gotten progressively more and more weighed down by physical ailments, but no solid diagnosis to explain the continued issues.

In the last 2-3 years we have started treatment for the following: asthma, seasonal allergies (thankfully no food allergies) and accompanying sinus infections. In addition to fatigue and aches, his most recent new symptom was a racing heart while standing around, or sometimes even when just lying around. Actually this is good in some way because it gets us out of the 'imagined' illnesses into the realm of real physical conditions. I know what you mean about the struggle to get help.

This last symptom kind of did the trick for me. Putting that together with his history of a severe viral illness at age 8 (which I'd already pegged as the 'beginning' of many of these issues) -- I found that there is a syndrome called 'POTS' which can be a result of a viral illness, exacerbated by rapid growth in teen years and dehydration/low salt intake. One symptom is major fatigue. You might look into it.

Per the cardiologist, who basically agrees this looks like a possibility after doing a heart rate monitor for a month, we have increased salt and water and removed him from any stimulant meds for his add (which weren't a big hit anyway, so that is not a huge loss).

His incidence of the problem with his heart rate is almost
zero now, however last week he was feeling pretty sick again and probably dehydrated and it started beating fast for a few minutes. I am of course watching his water intake again more closely.

This doesn't completely eliminate the fact that he *is* more sick some of the time, partly due to the asthma and allergies, so we are working on allergy shots to relieve that as much as possible ( they tend to make him feel worse sometimes too however). And monitoring his asthma more closely.

But the cold and flu season is upon us, and so he is missing many days this month so far.

We contacted a few of his teachers and they are 100% kind and helpful, so we have good hope that maybe we can just keep getting him his work and he'll be able to get it done. Academics are so far very good this year.

One concern is the P.E. course he was going to take this summer - we put it off in lieu of a life skills class which I think has been pretty beneficial.
It has a pretty high bar for completion of physical activities, so we are not sure whether to get an up front waiver of the physical part, if that is even possible, or just some kind of semi-waiver so that if he runs into health problems mid-way it won't keep him from completing the course.

If anyone has experience with this, please let me know.

Sorry this is so long, but perhaps may help others in the same boat.