What Is Causing My Dizziness And Headaches?

i feel light headed everyday, usually whn i stand up, and i have reall bad headaches everysingle day, sometimes whenerver i wake up it hearts behind my neck. and ihave hot flashes alot! and sometimes i get a really bad chest pain like im being stabbed and i have hear burn. i am only 12 and when i was 7 i had brain sugery 2 times. i had kiari 1 and scullyousis. i dont know if im sick or what?