Out of shape or something more serious?

[akimbo]

I know I'm overweight and out of shape, but I think I have risk factors for heart disease also.  Lately I've had reduced exercise tolerance (shortness of breath, sweating, muscle cramp type pain in my chest and back) which only lasts for a few minutes after I stop the exercise.  I sweat a lot even at rest, and I know I'm in bad shape, so I've just attributed the SOB and pain to lack of conditioning.  At my age though, I'm starting to worry about whether I have heart disease.

I'm 48, female, 5'6", 320 lbs (extra weight mostly in my belly and hips).  I've never been one for other kinds of exercise due to discomfort, and mostly just do walking - but I'm not even doing very much of that lately.  I take Nadolol for benign PVC's and HCTZ (plus potassium) for slightly elevated diastolic BP, both well controlled.  I also have a slight curvature of the spine (Scheuermann's disease) which has always seemed to give me chest discomfort on exercise.  

I have some medical insurance, but for historical reasons I have a large copayment that I can't usually afford, so I don't go to the doctor if I can't help it.  How can I find out what's causing my problems without having to do a whole bunch of tests?

[akimbo]

I accidentally mistyped my weight in my original question!  I weigh 220 lbs, not 320.  But I assume your points still stand, and I thank you for your response.

[Cleveland Clinic]

It is possible given your extreme weight and high likelihood of metabolic syndrome that you have well established coronary artery disease which is causing your symptoms. I can't fully rule it in, however, unless I subject you to some testing, such as an exercise stress test. This, if normal would likely argue against CAD as the cause of your symptoms, and if positive would probably prompt catheterization and possibly stenting.
In addition you will have to loose significant amounts of weight, which I understand is difficult because of your symptoms and weight, but caloric restriction can in most patients decrease their weight significantly. Once the cardiac tests clear you for exercise you can work on the other side of the equation, by increasing your energy expenditure through aerobic exercise.