Sharp pains under right rib cage?

For about the last 4-6 months, I have been experiencing sharp pain right below my rib cage on the right side. I am a 14 year old female. I know this is not ovulation because it happens at different times during the month. I cannot pinpoint where the pain is: it feels like a line right below my ribs running down to my hip. It is far over, being almost on my side. These pains usually begin when I am laying down on a bed on my stomach, and they refuse to go away until I have been standing for about 5-10 minutes. They sometimes start when I am sitting too, but never start when I am standing. They are less frequent than 1 time a week, though I am not exactly sure how often. thanks for any help or advice!