I'm sorry you had the need to seek out this site, but I'm certain you'll receive support and information that will help guide you and your husband through this together. There are so many wise and caring people here.
Post radiation treatment problems can be numerous. The damage is insidious, often clinically silent, progresses slowly and can continue long after the last treatment has ended.
Radiation Proctitis is a well known complication of radiation treatment for prostate cancer. My first suggestion is that you and your husband find another oncologist immediately for consult because you must first identify the cause of the pain before a proper treatment plan can be developed.
Where are you located? Are there any wound healing centers or hospitals in your area that offer HBO? Hyperbaric oxygen therapy has been used successfully to improve and sometimes completely resolve the symptoms of this difficult condition.
Keep us posted. You'll be in our thoughts and prayers.