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.