I hope you can get a complete check-up by a medical doctor. I general full physical with an electrocardiogram would be a good start.
Most heart problems come later in life than 20 years old, but that does not mean you do not have any heart problems. Get it checked.
True chest pains in someone your age would be extrememly rare as chest pain is caused by narrowing of the arteries or from something like a Hypertrophic Cardiomyopathy that was so advanced the heart walls no longer received any blood flow. Both of those heart problems, let's just say, you would be well aware of them. From what you have written, it sounds like you are having premature beats (which everyone has at one time or another). See a cardiologist if that makes you feel better.