Toprol-xl Inappropriate Sinus Tachycardia, Peak Flow Meter, Toprol Xl, Chest X Ray, Shortness of Breath

It seems as though a lot of people here have experienced what I have...shortness of breath, feeling like you can't get enough air, lightheadedness when standing, etc. I'm only 21 and on 50 mg of this sh**. The past 2 days I have cut myself down to 37.5 mg and hopefully this will help. Being anxious about not being able to breathe correctly makes it worse. I'm pretty sure the shortness of breath is not cardiac in origin as I have recently had a normal chest x-ray and echocardiogram. I even tried a peak flow meter to see if I had developed asthma, and my reading was 400, which is normal for my weight and height. 5'3, 108 lbs. I am convinced that it must be the Toprol, which I was taking for inappropriate sinus tachycardia. If I had some kind of cardiomyopathy (which causes shortness of breath) that symptom would be HELPED by taking the Toprol XL, as it would relax the heart. I want off this stuff, or at least reduced a lot.