Feeling fatigue, generally unwell and very irritable. what are some causes. also nausea and pounding heart.

Could be thyroid: Recommend a visit with your physician for a check up.

POTS?: Teenage female with tachycardia, nauseousness, ; fatigue has non-specific symptoms. Thyroid problems, anemia, and autonomic symptoms might be explanatory. Hyperventilation is also of concern. Postural orthostatic tachycardia symptoms are a rare occurance. What is needed is a basic physical evaluation and laboratory studies as part of a differential diagnosis. Primary medical doctors can discern.