I think i have heart disease?

I am a 16 years old girl and i do have an enlarged heart but i think i might have heart disease.. When i lay down or just go for a daily jog or what ever i get a sharp pain but sometimes a really bad pain under my right breastbone. It hurts and then i feel really nauseous and lightheaded. I have no idea why, maybe its anxiety. But also when i went to the doctor they told me that i had a heart murmur but she said it maybe caused by the fact that i have asthma and i needed a new inhaler. I really hope i dont because i love sports and i never want to give them up ever!! its my life :[