Whenever i breathe, i have a sharp pain on my heart's bottom or side or top.

Since you are so young the only wise thing you can do is to talk to your parents. Sharp pain around your heart can be consequence of trouble with breathing. Troubles with breathing can be caused by various conditions, including cold and allergies. If you have been sick lately this could be result of that but if you haven’t and this is something that lasts for some time than the only thing you can do is to talk to your parents.

They will take you to the doctor who will preform physical exam to determine what is wrong with you. After diagnosingthe treatment will folow and than it is just matter of time when you will stop to feel sharp pain while you breath. Good luck!