The characteristic feature of Fibromyalgia
is a muscle pain
mostly in neck, back, thighs, and hips. There is presence of specific tender points in these areas that trigger the pain. Along with this there is morning stiffness in the muscles, brain fog, dizziness and other neurological symptoms.
Since you are suffering from pain specifically located at the joints, and it started after the flu, the pains are related to the viral infection.