Hi, since your just 17 years old and going by the description of your symptoms it's unlikely that these are cardiac. Also you said cardiac evaluation was normal.
These could be anything from deficiencies of
vitamin D and
B12 to
thyroid related issues to aneamia (low Hb)
If you haven't got evaluated for all this then consider som basic tests
Next Steps
It would help to consult a Physician for detailed history and examination
Health Tips
Since you have mentioned repeatedly jn your description that symptoms are more when you think of them, try some relaxing techniques and healthy distractions.