I agree, time to check with a cardiologist. Sorry it happen so young in life, but at least that means you are checking early in the development of whatever is causing the symptoms.
Low blood pressure can cause one to be dizzy and to pass out, how low is your blood pressure, and did it used to be more "normal", or higher?
Take care and let us know what you learn.
The best thing to do is go back to the cardiologist and tell them that the pain is lasting longer. The only way they can tell what's going on is to catch it on a monitor. Then they can see what connection, if any, there is between your heart's behavior and the pain. Perhaps you're having vasospasms. Don't know. The fact that it's changed means it's time to be checked again. Don't let them tell you you're too young to have heart problems. That's not true. You may not have clogged arteries but you could have rhythm problems or valve problems. They need to check it out.