Wouldn't I at least have a weird heartbeat if it were heart-related? I've had my pulse checked quite a bit since the breathing issues started and no one has ever expressed any concern that it might be a heart problem. I should also add that I had a CAT scan to rule out blood clots in my lungs and the results came back normal.
My mother has me on her insurance until I graduate college, so she knows all these problems I'm having and she said she also had breathing problems when she was my age. But hers went untreated and they eventually resolved themselves. So that gives me a little hope that maybe I have something that is not serious.
ETA: I did a little research on heart problems that are characterized by breathing problems and a couple of the symptoms I display are those of heart failure, so now I think I am getting anxious.

But none of the causes of heart failure really apply to me - I've had my oxygen levels, heart rate and blood pressure checked more than once since this problem began and no one ever expressed any concern that any of it was abnormal (my oxygen levels were 98-99 percent at any given time). I know my BP is slightly higher than the normal - something like 123/80, so I can't imagine that would constitute hypertension, and I have never had heart problems before. It can't be my age - I'm only 20 and there is absolutely no history of heart problems in my family. I also know I don't have diabetes, arrhythmia, defective heart valves, and so forth.
I was just thinking, though...if this was something very bad, wouldn't it have gotten worse over time and not better? My breathing problems have gotten better since they started. When I first had them, I had chest tightness and pain, found myself much more short of breath (especially at night) and once or twice felt my heart beating very hard, where I could place a finger against my chest and feel a noticeable hard thumping that was my heart. I realize these are signs of heart failure now. Since then, though, the chest pain and the loud thumping have stopped and now I have mild but constant shortness of breath.
My problems are also not exacerbated by physical exertion - I can walk five or more miles in one day and then go home and play DDR (if you don't know, it involves lots of movement and is a good cardio workout) and I won't feel anymore out of breath than I did before I developed breathing issues.
In fact, just today I played DDR and I took less time to recover from the exercise than I would have about a year ago. Wouldn't a heart problem make it very difficult for me to breathe following physical activity? My problem is my shortness of breath remains constant but rarely worsens under any circumstances; whether I am at rest or I'm walking, jumping, or moving in general. When I went through bouts of severe shortness of breath, I was completely at rest. I was sitting and trying to relax...and yet I can walk six miles without resting and the only pain I'll feel is in my legs and feet (which is to be expected).
In any case, I will ask my doctor if he thinks it may be a possible heart problem because I don't want to have a heart attack - not now, not ever.