Sharp pains aren't typical of heart attacks or angina, in my experience. When I've had heart attacks, it is more of a pressure, like a weight on the chest. Same thing with angina, but usually milder. I think the best way to determine if you have a heart issue is to get nitro pills, and when you have a long-lasting pain, take a pill. Get ready for a big head-ache, but if the chest pain goes away you might have a cardiac issue. Troponin levels are very important in diagnosing a heart attack, in my opinion, but if you haven't had heart damage, the heart attack is more of a warning, like angina.
If your concerns are affecting your quality of life, ask for an angiogram, where a probe is inserted into your heart arteries and scoped, and you will get a very accurate diagnosis. If you go to the ER repeatedly, they will do the test for sure. Keep us informed.
The ecg and blood tests can't rule out a heart problem. The ecg has to be taken at the time of the episode and the troponin test will only register if actual damage was done to the heart muscle.
Due to your age the doctors tend to assume it isn't coronary artery disease and that can be bad for you.
Until the problem is identified it's safer to assume it's serious and go into the ER every time you have an episode. The more times you show up, the greater the chance they will find an answer.
I had my first heart attack at age 34, after a year full of tests that kept saying I was fine.