Advice welcome

Hi,
I almost feel a bit of a fraud here as we do not yet have a diagnosis but I’m kind of stuck as to who to speak to for advice so I’m hoping someone could help.
My son (now 13) has always struggled with physical activities, never been able sporty, could never get the momentum to keep pedalling a bike, struggled with stairs etc. I just thought he was a ‘lazier’ child.
About 41/2 years ago he started complaining of extreme pain in his legs and them going ‘jelly like’ after walking for about 10-15 minutes – I’m ashamed to say, I didn’t take a great deal of notice – he’d been diagnosed with hypermobile joints and tight hamstrings and I just thought he was ‘nagging’. Then when he started secondary school almost 3 years ago, and had to walk about a mile each way, he really started having problems, his legs started off with hurting, then going numb and finally giving way beneath him initially after around 10 minutes on them – this then became the norm after approx. 1.25 metres. After a short rest, the feeling returns, sometimes with pain, and he can continue a short distance again before it happens again. He was having to drag himself up flights of stairs also and his legs would just go beneath him for no reason, with no warning pain. I must point out that, as a non driver, although he has never been a sporty child, he has always had to walk everywhere – we live in quite a rural area and without a car he’s had to always just walk.
The Drs were dallying in, so, in desperation I sought out a hypermobility specialist and paid privately for him to see him – he was diagnosed with ehlers danlos syndrome and, smugly, along I went to the GP, diagnosis in hand, demanding the physio the dr had suggested.
This triggered blood tests (finally) which I happily accepted, knowing full well they would find nothing – he had eds which doesn’t show up in clinical tests! Only they did – they called me to say his CK levels were at 3000 and asked if he’d done excessive exercise (he hadn’t). They then sent him for EMG tests which came back normal.
In this time, he saw the physio who confirmed that he did indeed have extremely mobile joints, but also incredibly weak muscles. He also had a period where his legs just completely gave way beneath him and he could bare no weight at all for 5 days – totally out of the blue.
The neuro saw him, did some basic muscle strength tests and decided he needs a muscle mri and biopsy and requested a further CK tests. Despite the paed having told us that they were looking at muscular dystrophy, the neuro said his CK levels, although high, were not high enough for what they were expecting- the day after seeing him, he had another period of non weight baring abilty – this time lasting for 6 days – and the CK test was performed during this period – again coming back with raised levels.
My son can just about move around in the home independently, he has a ground floor bedroom to avoid using the stairs and school have changed his timetable so all lessons are now on lower floors. He has to use crutches for outside the home so he has some support when his legs go and has a wheelchair for longer trips.
Does anyone else experience something similar to this? Is CK level 3000 too low to be anything too worrying? Can you get ‘flare ups’ of md which would explain these periods of total weakness in his legs? Any advice is greatly receieved.
Thank you so much for reading x