What Causes Palpitations Of Heart Along With Pain In Chest?

I have been having heart palpitations. They sometimes last 13 hours and are over a 100. I went to the ER last night and they couldn t find anything wrong.. It makes my chest hurt and I get dizzy. I m 25 female and not over weight. Could this be A Fib? I m worried because they haven t stopped in over a week.