21 year old Heart palpatations shortness of breath fatigue

I am 21 year old male and all of this started about 2 months about ago
I would also like to add that i am a recovering Alcoholic.
I also used to use Amphetamines regularly
As of recently i have started having heart palpatations that occur during running walking it feels almost as if my heart is fluttering and i am dizzy and lightheaded alot and very fatigued I also experience shortness of breath and fainty type feeling. The other day i went for a run and by the time i got back i was so dizzy and my heart was pounding so hard i thought i was going to pass out it took almost two hours for my heart rate to come down from 100 beats per minute to 75 were it usaully rest. I most also note my blood pressure is usaully 120/70 at rest

The other night was the weirdest tho i was just sitting watching tv when all the sudden a palpitation came on. my heart rate shot up to almost 160 beats per minute and i panicked i started to shake could barely breath and felt like i was going to faint. So i Called a Cab and went to my local ER. When i got there they were shocked at my pulse rate and took me back and did and EKG and sed that if the EKG showed an Arrhythmia they were going to put my into the Code blue section and Monitor my Condition. But just as surely as they ran the EKG my heart rate started to come down and they sed everything looked fine. They kept me anyway for about two hours gave me some medication and fluids tho an IV ran some blood and urine test and a CT/Scan and sent me home.

I have also noticed that during mild phisical activity such as walking i start to feel dizzy and lightheaded.
And after phisical activity my heartrate rest at 110 beats a minute for almost an hour.

Anyway I eventually went to my GP and she ran basic blood test and urine test checked my thyroid levels checked blood sugar for diabetes liver and kidneys levels and even for HIV/AIDS Syphilis and HEP A/B/C. And Everything came back Normal. She referred me to a Cardiologist

Later on that week i see a Cardiologist And he orders another EKG, A 24 holtor Monitor and an Echo cardiogram.
And to my surprise everything comes back completely normal even tho i experienced symptoms during the Holtor Monitor.

It has been almost a week since and i still expierience symptoms almost everyday. It has sucked the l;ife out of me and i am always super tired.

I have to also note the only medical conditions i suffer from are Acid Reflex disease, Asthma, Seasonal Allergies and Ulcers all of which i take medication for.

Any input is greatly appreciated.

-best-