I had this happen as well also have high anxiety.... my chest hurt for weeks finally went to the dr and I had 3 ribs out of place either way go to the dr
The first thing you need to do Cat is to calm yourself down! I can tell you with probably 99.9% accuracy that you are NOT having a heart attack. At 15 years of age, you haven't lived long enough to have clogged arteries; that takes a minimum of at least 20 years and that 20 years would have to be spent living and eating junk food. About the only time you would have a heart attack at your age is if your heart walls were either too thin (congestive heart failure) or too thick (hypertrophic cardiomyopathy) where the heart walls no longer receive a blood flow. You would be very symptomatic, there wouldn't be any question that there was a problem. What you are describing sounds like chest muscle issue, not heart. Have your mom take you to your pediatrician if she feels the need to, but being diabetic, I'm guessing you are seeing a doctor regularly anyway. if you had the issues I described here, you would have a heart murmur or gallop, the nurse and doctors aren't hearing that at this point. Try not to worry yourself. Take care.
You need to work with your endocrinologist to get your blood sugar more under control.