Night sweats at 89 years old!

My father who is 89 years old has been having night sweats for over two years now and his regular doctor has found nothing wrong with him to date. We go every 3 months for blood tests and his sugar levels are fine as are all other results within normal range. He is taking 20 mg of Enalapril for his blood pressure and 10 mg of Aricept for his dementia with a multi vitiamin daily. He isn't on any other medication and feels great except for the night sweats. He has gotten all types of scans to rule out tumors and never sweats in the day at all. His hormones might be the issue but at 89, I don't think it is worth putting him on any other medication when he still is physically healthy. What do you think about this and what if anything else should I be concerned with for his care?