@krisjb1 — sorry to hear you have been blasted with medical issues your whole life. I, and a lot of people on these message boards, also have been. You are correct that when people can't see what you're feeling, it's even more frustrating. I empathize with you.
After reading your story, the only advice I can offer is about the brain MRI. I have had terrible tinnitus since I was 11 and shattered my eardrum. I'm 64 now and it's louder than ever in one ear, but feels like my whole head. I have had several brain MRIs over the years and none of them impacted my tinnitus. You do want to put in tight foam earplugs that they should supply because the banging in the machine is very loud and will bug you for a couple days if no earplugs. Like after you go to a overly loud concert. Wear ear plugs they supply to be safe, you'll be fine and will protect your hearing. Some places even provide headphones with music.
MRI tips. Not sure if you've ever had an MRI. Some people are claustrophobic in the tube. I don't love it, but I don't take an sedatives either. Mind over matter. The secret is to close your eyes before you go in and never open them once until you come out. Don't even peek. Then you won't get that closed in feeling. I've probably had a dozen MRIs. It works. Hope you get some relief soon.