I would definitely give O2, with a Higher flow rate, a try. Make sure your Doctors are tracking everything you use. If not keep your own calender/log.  this can help prevent missing something that may help, but never gets the chance to. This can happen by not titrating the med to an adequate dose. Or not allowing enough time for the med to work.
    This seems especially important with different combinations of meds used. It is time consuming and can be frustrating. It took about 6 months for some of my meds to really start helping.

    I posted (Nov 8th 2010/Cluster Headache specific) about my use of Narcotics. I did get some very good results. Make sure that any Dr. who may prescribe narcotics has been certified in pain management. Many people on this site are absolutely opposed to narcotic use. (Understandably so).

    When the Dr. who ran the Pain Clinic told me he has had some sucess with what he called "Methadone Therapy" I told him I was not at all interested because of all the horror stories, I had heard about long term narcotic use. He then , more thoroughly, reviewed my history. (My history was contained an inch thick stack of papers which had all my appointments. The dr. spoke into a tape recorder at the end of each appointment. He reviewed everything talked about, all medications including any side effects,results, good or bad and his and my thoughts and ideas.

    He then called me in for an appointment and asked if I would be willing to bring my wife with me. Prior to the call I had researched whatever I could find concerning "Opiate Therapy". I was chronic for so long. I became resistant to the meds that had previously helped, including O2. I had migraines that would sometimes last last for up to 6 days. I was getting 3-5 cluster attacks each day. (Mine have always lasted 3 hours). The migraines made me nauseous. If my migraine was bad I would almost always throw up when I got a cluster.(Clusters by themselves never give me nausea) Throwing up seemed more like a reaction to the severe pain of a cluster when I was was already nauseated from the migraine.
    Anyway, my wife said "I think you are at a point where trying methadone therapy makes sense. You cannot work, drive (most of the time), or do anything at all.) If we do this together and I closely monitor your behaviour and make sure you use the meds exactly as prescribed, it's worth trying. If it doesn't help or you have problems following the exact treatment the Dr prescribes. We can discontinue them. I will keep your meds and give them to you when you are supposed to take them."

   My wife was a CNA and always has studied and had a huge interest in the medical field. She could give me trigger point injections when I used them. I could always trust her judgement. The Dr. asked me to give him at least 9 months before giving up. He said it was important so that he could very very slowly titrate the meds. This would prevent the Euphoria one gets from higher dosages. It took almost 6 months to help. soon after that I was able to work again. (Not every day or all day, but once in a while 20 hrs a week, as long as I could pick the times. I was lucky, blessed, fortunate, or anything that means the same.

  After a lot of years my clusters required less medications. When I needed less medication, the meds I was using made me very tired. This made it easy to reduce the dosage. I am still unable to stay at work for more than a few hours.

  What has worked for me, could more dangerous then helpful, for you. You have many things happening with your health that I know next to nothing about. So please make sure your Dr. knows everything that is going on with you.

  I have the utmost respect for you and what you must be going through. I thought that I could relate to almost anyone suffering from long term or severe pain.  It seems that getting it under control may be very difficult and very complex.

   Please accept my empathy and my prayers for you, that will start this very day.
       MikeS