Mike- The thing that I would ask you in this situation is do you have a family history(father's side or mother's side) of EARLY heart disease, heart attack or sudden death? This means before the age of 55 for you father's side and 65 for your mother's side. This is a very important question for doctors and tells them ALOT of information.
If you DO NOT have a family history of early onset heart problems, then the problem is probably some minor tachycardia issues brought on by anxiety or from being out of shape. Lower you exercise intensity but go for longer sessions until you build up some endurance. Then increase your intensity level. (Just my suggestion. I am NOT a doctor. However from my experience even cardiologists want most of their heart patients exercising to some degree. I think that a lack of proper exercise is the number 1 health problem in the world. ...And yes, I need to exercise more too!)
If you do have a family history of EARLY onset heart disease, you need to be very aggressive about getting the proper testing and seeing a cardiologist. Although at age 20, you are going to have a real problem getting the doctors to take you serious about heart issues.
If it turns out to be anxiety issues (three anxious-sounding posts in six minutes suggest this) I would try meditation/relaxation techniques before medication. That is only my personal preference. You have to do want benefits YOU! You decide-don't let some stranger from the internet or a doctor who PUSHES meds make up your mind for you in this issue!
Some people do have hearts that like to get tachy from time to time. Usually it is not a problem. If you are very symptomatic, your doctor might have you give beta blockers a try. However that can sometimes make intense workouts impossible. ???? You would just have to give it a try and see how it affected you.
Do you have a high resting heart rate? My nephew did. It was 120+ even while sleeping. They did an ablation on him and the problem is solved. So that is another idea.
Good luck with you search for answers.