Normal ecg & ekg(stress) & chest xray. still having sharp chest pains and palpitations. also trouble breathing, what can it be?

Many possibilities: It seems that your heart is not the issue here; however, you could still have some lung issues or even esophageal issues; talk to your doctor some more;

Lots of things : could be many things: pericarditis, costochondritis, nonspecific musculoskeletal pain, pleurisy. The point is, lots of ailments can cause these symptoms, many of which are uncomfortable but not dangerous. First order of business is ruling out "dangerous stuff", then the next step is learning how to cope with the process if it persists. Contact a reputable doctor to work through this.

Relax: Heart palpitations are the feelings of having rapid, fluttering or pounding heart or skipping heart beats. Although heart palpitations can be worrisome, they're usually harmless and rarely caused by a medical condition. Heart palpitations are more likely triggered by stress, exercise, and/or medication.The irregular beats associated with palpitations can usually be detected by a holter monitor.

You are 20 years old: and I do not expect some serious heart condition or lung trouble at this age give you those symptoms. Most probably it is your nerves, even could be an anxiety attack or panic attack. If an echocardiogram was done it would be nice to rule out mitral valve prolapse. You also probably needed a 24 hour holter monitor. Anyway I suggest to you to see a doctor in urgent care if you can't get your doctor