I'm A 20 Year Old And I've Been Having Chest

I'm a 20 year old and I've been having chest pain for the last two days continually and the last week or two off and on. It's extremely dull and right at my sternum. I have no other symptoms at all. I'm only 150 pounds and almost 5 11. Is this a heart attack or more likely a muscle that was strained from excercising. It doesn't feel like a normal sore muscle though.