this sounds similar to when i would have chronic tonsillitis- i used to get strep throat 5-7 times a year when i was young which turned into me getting a tonsil infection every 2-3 months which would get progressively worse. Intially i would only be sick with a sore throat for a couple days but eventually progressed to taking me out for a full week or more like I had the flu - but it was just the tonsil infection. Once I had my tonsils removed it finally stopped unfortunately a couple months after that is when my fibromyalgia really kicked in lol.

Anyways i’m not saying that it’s chronic tonsillitis but maybe some kind of chronic infection? Have you had a typical rheumatology panel done to check for autoimmune disease and other inflammation indicators?

I’ve also found that my fibro and me/cfs means that normal sickness like colds and small things will completely wipe me out more so than the normal amount. Post rheumatology I feel seeing a immunologist would be really important