I'm sorry to hear about your issues and hope you get to feeling better. I've seen perfectly healthy people—before and after COVID—who literally had their life

I'm sorry to hear about your issues and hope you get to feeling better. I've seen perfectly healthy people—before and after COVID—who literally had their life changed due to a completely random infection or issue. People who went deaf after having a baby or developed T1 diabetes. Some people were "perfectly healthy". But some people seemed healthy until they weren't. One day, their eating/drinking/smoking habits caught up with them due to age or complications from things they didn't even realize were health problems until it suddenly became an issue. I am not a doctor... but you mentioned weightlifting... the fatigue and neck pain could be a pinched nerve? Perhaps an injury that manifested itself after a viral infection? Have you seen a physiotherapist? I finally saw one about arm pain and it changed my life.