What Causes Sudden Pain In Head While Sitting Or Standing?

hi i am wondering if you can shed some light on a problem i have been experience for bout three months. the symptoms appear through out the day.If i sit down for a while and stand up (even slowly) i experience really bad pain in my right frount side of my head.on a scale of one to ten i would say 9. it feels as if some one is squeezing my brain and head together. i am on no medication and i am 21 female. i have no idea what it is and the pain persist for bout 4 seconds and completley dissapears when i sit down. the only way to stop the pain when standing is to bend forward or sit down. could you please advise me on what this could be , ithought it may be related to blood pressure?