I had 24/7 oxygen for a while too. They tell you to take the oxygen full strength when you start to feel a cluster coming on. It worked for me about 30% of the time. The only thing that worked for prevention was the steroid prednizone but I was told to take massive doses, even to dangerous levels monitored by my neurologist. But at least it was finally something that worked. I had a nerve block injection where they stick 3 inch long needle into the back of your neck to block pain for a while, for some well needed relief. Problem was, that didn't really work on me. I was at the final stage where they were considering doing a nerve removal surgery when we discovered that steroids would work. I'm so glad because of the known side effects of the nerve removal, including possible facial drooping from the lack of those nerves. I consider myself very blessed that I didn't have to have the nerve surgery, and got through to the point that I no longer have massive clusters, but still little short cluster periods with comparatively minor headaches.
I have been taken to emergency rooms with massive clusters in the past too. All they could do for me is a knock out injection, but it was needed to stop the damn marathon cluster.
Sorry to hear you had to suffer with that too. I've been told it's a pretty rare condition that only effects certain people, I guess we're among those who were stricken with it.
Clusters destroyed a lot of my life.