I've been having sharp intense pain know my heart/sternum that goes to my neck. I'm 20 years old, what could this be?

??? "sharp, intense pain" needs to be evaluated by a doctor, possibly emergently in the er! even though 20 is young and low risk for heart attack or dissection, soft tissue disorders or genetic high cholesterol or obesity might put you at risk, even at age 20. See a doctor!
Go in. While young people aren't usually at high risk for heart attack or aortic dissection, it is possible. Sometimes people get spasm of coronary arteries, which needs to be treated. Only a physician can clear this up. Many people who go to the er are not having heart attack. Better false alarms than having people die unnecessarily. At worst, you'll get a checkup, something young people often lack.