Medical Mystery - Can anybody help?

My current symptoms:
Extreme fatigue and tiredness throughout the entire day
Dissociation / feeling of faintness
Extreme mental fatigue and brain fog
Trouble concentrating and poor memory
This all started when I was 15 years old. I was in the gym when I started feeling a little lightheaded and weak and decided to go home early. It was nothing alarming; I thought I simply hadn’t slept well or hadn’t drunk enough water. However, from that day on, the symptoms listed above slowly became more and more apparent day by day until about a month later I completely stopped working out and started seeing doctors for it.
Over the last 7 years I have done every test under the sun. I could not count the number of blood tests, MRI’s, x-rays, urine tests, stool tests, ultrasounds, ECGs, PFTs etc. that I have been through. I have been to neurologists, cardiologists, pulmonologists, gastroenterologists, endocrinologists, internists, osteopathics, etc. Every organ in my body has been examined thoroughly and not one single doctor has found the cause of my symptoms. As far as the tests are concerned, I am a healthy individual. If there was a deficiency in some test value, I supplemented it until it was normal and it did not improve my symptoms.
I want to make clear that this is not simply a level of fatigue that is uncomfortable; it is entirely debilitating. I have stopped doing several activities because I physically cannot keep up. There are days where I skip plans with friends or don’t even leave the house because the feeling of fatigue is so extreme that I feel like I will pass out or collapse.
I have never actually passed out from the cause of these symptoms over the last 7 years, but the feeling is constantly looming. There are times when I am simply sitting in a room with people and suddenly feel so disconnected from reality that I need to leave the room and go to the bathroom in fear of passing out in front of everyone.
I have also gone down the psychological track. I was diagnosed with general anxiety disorder in late 2018 and have been taking Cipralex for it. I have felt significant improvements in my anxiety levels since then, but not in my other symptoms. I manage to exercise around 5 days per week, although I do this at home (out of fear of passing out at the gym) and it is an absolute battle to even get in a 45 minute workout.
Some other important information:
I am a 22 year old male, 198cm tall and 95 kg
I don’t drink or smoke or do any drugs
I have no vitamin / nutrient deficiencies which would cause these symptoms
I am currently trying to get a sleep study done because I feel like I get terrible sleep
Does anybody have any clue at all what the cause could be? Maybe you know of somebody with very similar symptoms that has gotten a diagnosis or have any idea of something else I could investigate / test for. Any help is appreciated.