Hi @mpearce1959 Sorry it took so long to respond. I have no personal experience with sleep apnea but I understand what is involved.
Three months after radiation (I am assuming radiation) means you are about one-eighth healed from the effects. It generally takes a good two years to fully recover after radiation therapy. After that point you likely will have internal scar tissue forever. These things alone can contribute greatly to sleep breathing difficulties as many of us can attest.
My experience, I slept upright initially, then with head elevated and always on my side for well over a year in order to breathe better at night. Never had a sleep study aside from my wife telling me I am sleeping better now and not choking.