Anyone tried Pizotifen? (In australia sold under the name Sandomigran. This was a starting point, to take 0.5 mg nightly. He referred me to a neurologist, although to be honest I didn't feel the doctor I saw today knew anything about POIS - he was well aware of post O migraines, but nothing like what I experience. He seemed confident that an endocrinologist won't be helpful, and that based on my symptoms, a neurologist is most suitable. At least he said he believed it was a real condition.
One piece of advice he gave me was before you ejaculate, try putting your head down, like you are facing the ground. He said for that often significantly helps some people with sexual headaches.
Who knows...