hi,
thank you for providing the brief history of you.
as you mentioned your tests were normal and almost all is fine. But still you feel tired,
fatigue, lack of energy etc
Since you have been visiting the cardiologist you can discuss to him about doing
physical therapy.
Focussing on strengthening conditioning, Breathing exercises, core stabilitu etc will help.
Based on the symptoms what you have mentioned your metabolic activity might be slow, so that is the one reason for lack of energy, faigue,
tiredness etc.
also you mentioned that you feel tightness in chest , for which you can perform regular breathing exercises which will help to have adequate
oxygen in the lungs.
also core stability exercises will help you get good strength.
If the symptoms persists you can take advice from a cardiologist.
With the grace of God I wish you a good health.
Regards
Jay Indravadan Patel