chest x-ray and ecg to rule out cardiac and respiratory problem.
it might be due to gastritis
, but you have not mention any gastric complains.
so posibility of anxiety
disorder can be there,
is there any stressor??
have you any thought about nature of illness and prognosis and excessive worries about it??
have you any depressive feelings??
have you any big social or financial problem??
if it is due to anxiety then anti anxiety medication( sertraline
) and counseling is helpful to you.