orgasm headaches

I have had almost the same thing recently as well.  It's been happening for about 2 1/2 weeks now.  The first time it happened, I had this explosion of pain coming from the back of my head and moving forward.  It happened just as I orgasmed.  After this initial experience, it has happened every time since, but now the pain starts as I begin to get closer to orgasm.  Sometimes the pain is so great I have to stop.  If I do continue, I get the same explosion of pain from the back of my head.  The intense headache lasts for at least 10 minutes and just a general bad headache lasts for hours afterward.  I have done a bit of research and it seems most people's headaches diminish within the hour after, but mine do not.  I also know that I am breathing plenty, so that is not the problem.  I have no idea what is going on.  Does anyone have any ideas?