OP, I’ve only read your posts, so apologise if this isn’t appropriate.
I’ve got long Covid and have been involved with this community. If I’m right, your son had Covid last year?
If this was my son, and I could afford it, I’d take him to see one of the cardiologists privately, probably in London, who have developed interest in the effects of Covid.
The long Covid community talks a lot about Dr Boon Lim and Dr Opel, but usually in the context of dysautonomia , so may not be the right people for you.
One way I’ve found the best doc to see is by looking for those who advise support organisations. For example, I had tummy problems. My GP wanted to refer me to a gastro who was a surgeon. I did my research and found the doc who advises the Inflammatory Bowel Society (that’s not the correct name!) as that’s more where my symptoms lay. Luckily for me he practised in my home town. Went to see him. Paid for colonoscopy and got my proper diagnosis.
Another time I was in an injury compensation situation with a damaged shoulder. Other side’s insurance company wanted me to be assessed by a knee specialist. No thanks, I said.
For my penny’s worth, going to uni in September is an absolute non starter.
good luck.