Got some good news at long last
Looks like there's hope for treatment of my illness. In roughly 1 month I'll have the results of my DNA test that will confirm the specialists' diagnosis or rule out the disease (CPT-2 deficiency) they're testing for. Either way they detected a strong deviation of my carnitine levels in my blood so that's the main problem. Carnitine is used in supplying energy to the muscles so due to my lack of carnitine my muscles can't properly utillize energy.
My mom was doing some online shopping for protein powder and noticed the site also had a carnitine supplement so she bought it to see if it could help.
Not sure how I hadn't thought of this earlier but it does in fact work. Normally I am only able to perform 5-6 squats (no weights) before my muscles fully cramp up and give out. I've been taking the carnitine supplement for a few days now and I can now do 15 squats. I'm still exhausted by the end of it and my legs are still stiff a day later but it's a pretty significant improvement at least. It doesn't seem to affect my chronic pain in any way but I can now perform a few more activities without being utterly exhausted.
I can finally talk somewhat normally again without having to catch my breath every sentence and I can do some more household tasks (cleaning, ...) without requiring assistance.
It's a small step forward but this has given me some hope again. Maybe one day I'll be able to ride my bicycle again.