Our nervous system is wired a particular way during embryology, and this is the word:
If chest pain occurs when you breathe or stretch or change position, it is *NOT* related to your heart.
For more information, you can google something like "compare visceral and somatic pain."
It can be difficult to distinguish chest pain due to a heart problem from other types of chest pain.
However, chest pain that gets better or worse when you change your body position or that intensifies when you breathe deeply or cough is less likely due to a heart problem.
Your chest pain is probably from muscle or bones.
It can have its origin in the cartilage of your rib cage, particularly the cartilage that joins your ribs to your breastbone, or in sore muscles or from a bruised or broken rib.
When pain comes from the heart itself it is normally not a sharp but rather a dull pain or a feeling of pressure on the chest.
At your age, heart problems are very rare.
If the pain persists or worsens, go see a doctor to be sure.
Hope that someone have some advice. Thanks!