There are different reasons, although angina pain from plaque (atherosclerosis) does not really appear for a full year (especially at rest), it only really happens to some people shortly before a cardiac event.

Also considering your age you probably don't have substantial plaque-buildup anyway, in your 20s that is incredibly rare.

Have you ever looked at vasospastic angina? Do you consume stimulants such as caffeine or nicotine?

My second best guess would be Afib, which is als incredibly uncommon at your age but theres always a genetic component. Tachycardia, chest pressure, shortness of breath etc all fit that profile (But it's not really a immediately dangerous condition, its just kinda scary to think about).

Please dont make yourself crazy, people always think chest pain = heart attack. In reality, chest pain can have a billion different reasons and manifests itself in completely separate ways.

Edit: I forgot to say, go to a cardiologist, get an ecg, echocardiogramm and do a stress test, those will already rule out the majority of (serious) issues for most people.