Constant Headaches, Breathing issues, memory issues, what is wrong?

It might sound crazy, but I am a 15-going-on-16 female with symptoms affecting my life, and I am terrified this is all in my head. I have constant breathing issues, constant tension headaches (centered around the back of my head and eyes), brain fog, memory issues, and my memory has gotten so bad I can't remember spoken words, at all. I can't remember parts of my days, and while I do have anxiety, I am starting to believe the constant pressure on my chest isn't from that. I am struggling so hard now and I don't know what is going on, and these symptoms started off really mild two and a half years ago and now have gotten to the point where it is becoming unlivable.
Notes on Medical History:
0. Have a chronic autoimmune medical issue that caused increased fight-or-flight (not MAST, doctors cannot determine it, genetic), but upped my medication for that, helped with the weird restlessness and back pain, but did not help with the breathing or other issues.
1. Genetic relatives with a history of thyroid issues, particularly hyperthyroidism
2. Have been diagnosed with potential arrhythmia of the heart when I was seven
3. Was diagnosed with GAD at 8-9ish (My memory has always been poor, but never this bad - I am missing 3 hours worth of memories at a time). Also have been diagnosed with long-and-short asthma in Australia (in America I was fine- where I was living in Australia, everyone has asthma), and no matter how many puffs of flixotide, Qvar, or Ventolin, nothing helps. Also got glasses for myopia, (oddly my vision improved after fainting, and on an interesting side note, my eyes are specializing, my left for short-range and my right for long-range.)
4. Fell on my back off of a swing after just turning 13, in April. I couldn't breathe for 30-45 seconds, and turned red, but was able to walk and talk totally fine, after I caught my breath, although my voice was a little strained. Back did not bruise but was sore for a few days afterwards.
5. In the end of June to the beginning of July of that year, I began noticing issues - I could not run as long or as fast as before. I couldn't get enough breath, which by the way, really, really hurts. My legs could move, but not my lungs. However, I also learned to swim during this time, and surprising, could swim with no issues respiratorily.
6. By December 2023, I could not run. I felt like I was dying, the pain was so bad, and my vision started tunneling. Memory issues began, and random back pain also began.
7. Memory issues many dealing with the comprehension of spoken words rapidly deteriorated, to the point at the end of 2024 I could not follow 2-step instructions, either because I was trying so hard to remember the first, there was no space for the second, or I forgot the first by the time I remembered the second.
8. Early 2025 after walking a lot, or dong exercise that requires respiration, about half-an-hour after doing the exercise my heart begins beating out of control. I can feel it just start to beat really fast, erratically, and hard, and it hurts. Additionally, at around this time, I have to start taking conscious breaths every 10 breaths, or I feel like I am beginning to suffocate and then I spiral. Also, if I am under too much stress, I faint.
9. Mid 2025 I cannot sleep through the night because I wake up having forgotten to breathe, and I begin to forget written words. Previously, written words I have had a near-photographic memory of, like to the point where I could recite a poem I read from memory. I could quote book passages.
10. August-November: Focus is a memory that is very faint. My grades suffer and I forget all the chores I need to do, and there is only about 3 per day. In addition, my lower back hurting becomes unbearable when I am tired, and after a while of sitting up straight, goes numb, which causes my legs to fall asleep. Fainting continues.
11. Late November-December - I increase my dose of Mirtazapine to 30 milligrams from 22.5. Back symptoms cease, as mentioned, and restlessness and phantom aches are less. Memory continues to deteriorate, and so does my focus, and my headaches and chest pain are near constant. Lying down does not improve the headaches, but it does the chest pain.
Further Notes: No x-rays, no tests, I have no idea where to begin, and right now I am concerned this is just me being overdramatic. Health insurance is not great, and we aren't rich, so I can't get it wrong.
I am so sorry for the length, but I thought it would be best to be as detailed as possible.
Edit: Forgot to mention COVID. I don't think I have ever gotten it, as I have been very careful (immunocompromised), and I have gotten Pfizer and Moderna vaccines, so I don't think it is Long COVID.