If I were you I would converse with his dr's about this. Based on my experience it is not thyroid if he has no other symptoms. (I have been through a low thyroid problem and it makes you feel very crappy but no Viagra was required) The radiation didn't cause a problem for me either but you should ask the radiation dr.

Pain meds will sometimes but you have ruled that out. It is such an important thing (usually) in a marriage that I don't think you should wait. I could imagine it is something he needs to address through therapy.

You don't mention his age but he is now 2 years older and this could be a problem totally seperate from the treatments. Fortunately there are things you can do about it.

Take care

Mark, 21 Year survivor, SCC right tonsil, 3 nodes positive, one with extra-capsular spread. I never asked what stage (would have scared me anyway) Right side tonsillectomy, radical neck dissection right side, maximum radiation to both sides, no chemo, no PEG, age 40 when diagnosed.