I was diagnosed with migraines a couple of years ago but these headaches aren't migraine headaches. Plus the stiffness is the biggest problem really.
Apart from that the doctors haven't really been very helpful.
Possibly an underlying low grade infectious condition playing" hide and seek"
with your immune system.
Some pathogens can hide deep in tissues, some for life, away from the blood circulation and only when the immune system is overwhelmed, they become
active and cause infections along with many symptoms.
You did not mention if you had any tests or prior diagnosis.
Take care,
Niko
It could be an extreme for of stress, or an autoimmune disease, what are your other symptoms.