NSVT is short for non-sustained ventricular tachycardia -- basically, it is a short run of extra heart beats that initiate from the bottom chambers of the heart and self-terminate, allowing the normal pacemaker of the heart to take over. Basically it is a string of PVCs put together in series. In a structurally normal heart in a young person, this really doesn't mean very much. If it is going to cause symptoms, it usually causes palpitations, or the sensation of your heart fluttering or skipping a beat. If the NSVT is long enough, it could cause lightheadedness or dizziness. If you want to assess whether this accounts for your symptoms, then you should wear another monitor and document when you have symptoms so that those times can be correlated with any changes in your heart rhythm on the monitor.
Also, I want to add that when I run, I get a really sharp/dull painful feeling in my chest. Could that be NSVT while I'm running?