The long duration of the pain rules out any acute or serious pathology straightaway.Right upper abdominal pain
may arise from liver,gall bladder
,supra renal gland and colon.Clinical examination and USG abdomen may provide a clue, if there is anything wrong.Thorough breast examination may be required to rule out lumps and also inflammatory breast conditions like mastitis
.But even if it was any of these ,you have not have been so comfortable for so long.In your case it is more possible that it is something like costochondritis
.This is a benign condition and requires only intermittent supportive care with analgesics for pain relief.