I'm afraid you've stumped me. I've seen patients who sweat on the forehead after eating spicy foods, but I haven't seen, or heard about, people who sweat profusely on their heads all the time. I also can't figure out what CPAP, oxygen levels, or vitamins have to do with it one way or the other. There are instances of severe night sweats associated with internal diseases, but these involve sweating all over, not just on the head. You also don't indicate whether the problem is recent, chronic, or lifelong. I advise you to consult your internist or dermatologist in person. Maybe physical examination will provide some clue.
Best.
Dr. Rockoff
Dr. Rockoff