There is a list here of recommended doctors for CH: https://clusterbusters.org/cluster-resources/ It's not updated or complete, but if you can find someone on this list, you will be better off. Many/most neurologists don't recognize CH, and when they do, many/most make terrible prescriptions (not prescribing oxygen, for example).
Some of his symptoms sound like they might be hemicrania: "Hemicrania continua is characterized as a continuous, strictly unilateral headache of mild to moderate intensity with superimposed exacerbations of more severe pain. During these exacerbations, one or more autonomic symptoms (ptosis, conjunctival injection, lacrimation, and nasal congestion) occur ipsilateral to the pain. Many patients report a foreign body sensation, like an eyelash or a piece of sand, in the eye ipsilateral to the pain. This headache is defined by its absolute response to therapeutic doses of indomethacin."
Here's something I'm absolutely not sure about. This is all speculative. I think you might be able to contact a local blood test provider and get a vitamin D test done. You could look up "blood test provider" on google and call one. They might not take insurance, but the cost might not be much more than the online D test, and the results would be considerably quicker (you're looking at at least a couple of weeks to get the online test, return it, and get the results) and more reliable. [EDIT: Looking back at Denny's post, I see that the process he's describing is potentially quicker than the one I was thinking of, where you order the kit online, it gets mailed to you, you put some blood on it, mail it back, and wait for results. But maybe what I'm suggesting would skip the middle man.]
My daughter has CH. It is very difficult to deal with that as a parent. THANK YOU for doing what you are doing!!