Hi friend,
Welcome to Health Care Magic
     You need investigations – 
      You have not stated your personal habits, family history, or co-morbidities, even age or gender...which could influence the diagnosis and outcome...
     Anaemia / Anxiety / Alcohol / Tobacco (smoking) / Caffeine (too much tea, coffee, cola) / Fever / Infection / Pain / Stress / Thyroid / Vitamin D, calcium, magnesium / Medicines like 
Phenylephrine used for ‘cold’; 
Salbutamol used for asthma and so on - may be responsible.... / Illicit ‘drugs’ like 
Amphetamine are notorious to cause abnormal beats /  At times, abnormal nerve paths in the heart (bypass tracts) or disease of the conduction system may be responsible!      
ECHOcardiogram is necessary to see the heart valves (
Mitral Valve Prolapse) / heart muscle (
Cardiomyopathy) and heart function (
Ejection fraction, wall motion abnormality) / clots...
       TMT – Treadmill exercise ECG; may be with thallium isotope – is necessary to evaluate ischemia (reduced blood flow / Coronary Artery Disease)
      If there are no clues and if the problem is still bothering to the extent of interfering with life style, you may need Electro Physiological Studies (EPS) > it resembles angio – a catheter is put inside the heart / electrical activity recorded / stimulation and suppression tests are carried out / suitable medicine tested and so on.  Though the test is the gold standard, it is INVASIVE and is not generally done unless there are compelling indications.  This super-speciality expert is called ELECTRO-PHYSIOLOGIST.   The treating doctor may suggest them depending on need, based on his assessment of the situation.  / There are other advanced treatment modalities - like ablation (thermal or radio-frequency), which could be done during EPS.
Take care
Wishing speedy recovery
God bless
Good luck