It's difficult to say without seeing the ECG and having complete history and exams.
The ecg numbers are mostly normal except for the heart rate of 126. Given that you have a PR interval that the machine can pick up, i would say its probably not Atrial fibrillation or some other SVT. Sinus tachycardia >100bpm especially prolonged is pathological unless you are being stressed (ex. exercising).
I'm concerned for pulmonary embolism given chest pain, shortness of breath and HR 126bpm. A pneumothorax can also give you similar symptoms and tachycardia.
They gave you the aspirin and nitroglycerin pills as precaution for potential heart attack but very unlikely assuming your are born in 1984 and are healthy without other risk factors.
If symptoms haven't gone away and your pulse rate is still fast, see a doctor again for a scan of your chest if one has not been done already. A thyroid level would also be useful especially if the a chest scan was normal.