Got a few questions for you.
1.Does your spine or shoulder blades hurt?
2.Is the pain located directly in between your chest and your stomach?
When I was 15, I had gallbladder disease, where these things called gallstones, calcified bile, formed in my gallbladder and got stuck in my bile duct to my liver.
Long story short, I needed surgery and I had EXCRUCIATING pain!
If you have pain in your spine or shoulder blades, and pain right in between your chest and stomach, please go to either your primary doctor or the ER and request to have an ultrasound done! (It took the hospital 3 times to find out what was wrong with me!)
Although it is rare for a 15 year old to have gallstones, it isn't impossible!