A 40-year-old woman presents with a 6-month history of fatigue, generalised aches and pains, and 'brain fog'. Blood tests including FBC, U&Es, LFTs, TFTs, CRP, ESR, calcium, vitamin D, and coeliac screen are all normal. Examination reveals multiple tender points over her neck, shoulders, back, and hips, but no joint swelling or inflammation. According to NICE NG193, what is the most likely diagnosis?