A 42-year-old woman presents with a 6-month history of fatigue, generalized aches and pains, and 'brain fog'. She sleeps poorly and wakes unrefreshed. Examination reveals multiple tender points at specific anatomical sites, but no joint swelling or inflammation. Her blood tests including FBC, U&Es, TFTs, ESR, CRP, and autoimmune screen are all normal. What is the most likely diagnosis?