It's like a dull ache in my chest, and sometimes it's a stabbing pain. It's hard to breathe and I can really tired after walking short distances, to the point where I have to sit down. Just a few months ago I was an athlete, and now I keep losing weight and everything hurts. 

I've gotten a heart scan or whatever and I don't have an irregular heartbeat, but I did used to struggle for Anorexia. Please help.