Ok, I'm 21 years old. I have chest pain that comes from different things. I've had ammonia before? Don't know if it's breast cancer or heart problems.

This is my advice to. My advice to you is not to think of worst possible causes for your chest pain, like you have listed here. You do not have breast Cancer or heart problems at this young age. If the pain is persistent after 2-3 weeks, you should go see your doctor and have him/her check you with a complete physical examination. If there is any serious concern, he/she may order some tests to make a proper diagnosis.