Linear infiltrates in apical region of lung mostly suggests Tuberculosis
, you donot have weight loss
, no blood in cough , non-smoker and non-addict , still this can indicate Kocks disease
Linear infiltrates could be due to backache
problem known as Ankylosing spondylitis
I would recommend a sputum report , mycodot test for TB , ESR and montoux can give us more clues for TB.
Hope this helps.