The low level of the "normal" range of vitamin D [25(OH)D] is 30 ng/mL in the US. "Batch" (who has developed, improved, and closely tracked the D3 regimen) says this in the document I referred you to: >>CH'ers who have used this regimen and experienced a significant reduction in the frequency and severity of their CH or gone pain free and then had this test have had an average 25(OH)D serum concentration of 81.4 ng/mL. min = 34.0 ng/mL, max = 149.0 ng/mL.<< So you might be in the normal range but still have a "deficiency" regarding treating CH.
Because so many people with CH get relief from O2, and because it is very very rare for anyone who tries high flow rates (25 lpm or more) with a good mask (such as this one: http://www.clusterheadaches.com/ccp8/index.php?app=ecom&ns=prodshow&ref=clustero2kit)to not have success, and because O2 makes such a huge difference, I would urge you to give O2 another shot. You'd have to buy the higher-flow regulator and the mask, but it might be worth it.
And please don't completely dismiss busting.