yes, get oxygen. yes, consider busting preventively during the year. definitely start on the D3 regimen, which will be as effective preventively (for future cycles) as the verap.
just a few more words on the verapamil. first, it takes some weeks to get into your system, so if you can realistically anticipate a one-to-three-week cycle, there would seem to be no point, or very little point. prednisone is sometimes used as a "bridge" to quell the pain while the verap is taking effect. there are things to be said against prednisone, and using it more than once a year is strongly discouraged, but it could be considered, i would think, for cycles so short. except, as you say, why risk poking the bear.
(also, verap dosage has to start pretty low, to make sure there are no issues, and then it should be monitored as it is increased. in such a very short cycle, it is very unlikely to help, and you don't want to be on it year-round in your current situation.)