What can cause severe stabbing heart pains that come and go for months to a health 19 year old, with clear ekg, echo, bloodwork and holter, plus the feeling of constant palpitations?

The most common issue is an area just to the left of and behind the heart where the swallow tube joins the stomach. The backwash of stomach acid can create sores/irritation that can cause pain and spasms. The term reflux is often uses. Avoiding nicotine/caffeine/spicy foods often helps reduce symptoms. A thorough history and exam often supports this label,

If all of the above is normal, you can try treating for reflux as Dr Ferguson suggested; however, another possibility is stress/anxiety; that could cause all of your symptoms with all normal testing. Please discuss both of these possibilities with your doctor if you haven’t already.