middle of my chest feels tender under rib cage

hi Im 14 years old and just below my rib cage in the middle of my chest it feels tender and horrible when I touch it.Also it is really uncomfortable and always there I have to put my hand over it just because its so uncomfortable its not sore I only felt a stabbing pain once when I woke up. Please tell me what it is please I am really scared its something to do with the heart. Also I do not eat fruit at all I drink absolutely huge amounts of milk its all I drink, I do not smoke or drink and do not eat many sweets or chocolate and I get plenty exercise. Please tell me if its serious ill be so grateful ive had it for about 3 or 4 years or maybe more. And please give it to me in a way that I understand I dont get all those medical terms please ill be forever grateful