depakote for migraines and new type of headache?

Hello and thank you for your help. I am a 37 year old female with a long history of migraines.  Over the past few years my migraines have gotten increasingly frequent and more intense. I presently am on Depakote-500mg daily for prevention and have been on it now for about two months. My migraines are definitley getting less severe and less frequent but for the past week am having a severe sharp pain every evening in the back of my head that I can feel in my neck as well and somewhat on my face. THis feels differently than a migraine and does not come on gradually but suddenly  It feels like a sharp knife like pain that stops me in my tracks completely but goes away in about 15 minutes. Sometimes after the pain goes away,  I become very dizzy and have to vomit.  Any thoughts what this could be?

thank you  

p.s.= I was experiencing the nausea and vomiting when I first went on the meds and the dr. checked my liver and it was okay.  Just take prevacid now and that has helped somewhat.

[Eddie1994]

I would consider such symptoms to be a medical emergency and would visit a ER ASAP to be on the safe side.  Good luck.