I am sorry that you are dealing with this right now. In my experience with anxiety, especially when we worry about our health, I tended to focus on what I thought might be a problem. My concerns were with heart health, so naturally I would focus on every little palpatation, twinge, pain, etc in my chest; and it drove me up a wall. Your doctor says that you are okay, which is a great thing by the way, but that sometimes does not reassure us when we think something is wrong. Plus, you are really young, which is also a good thing:). Now, do you have access to counseling? For me, just talking about my worries and understanding why I was thinking the way I did, helped me overcome this...keep us posted!
Yes it is actually very common for anxiety to cause the heart to hurt! Like cj29 says, we are not easily convinced that worrying can cause a physical problem like pain in our heart for example. I have experineced the same thing, and thought it was a physical disease, until I learned it was my own worrying, anxiety. Hope you're feeling better.