Odds are with a healthy heart which your ecg and ultra sound seem to indicate you have you are not dieing. It sounds like you have some pvcs. They can hurt and they can cause my chest to have some pain as well though it won't last but maybe 10 minutes and go away. That said, if this is concerning you then I would push to get a monitor to get what you have captured so the doctor can see exactly what it is. It it wasn't happening when you had your ecg done you will have to try and catch it with a monitor you wear for either a day or month. It is likely what you are sensing is nothing more than a nuisance that you will need to get use to as pvc though disconcerting are harmless but considering you aren't exactly sure what you are sensing and you are experiencing some pain it is best to get it properly diagnosed by a doctor. Good luck and keep us posted what you find out.
What is "a lot" to you? If you mean premature beats like PVC's, thousands a day is a lot. I average 1 to 5 minute and it's not consider a lot. When I had a period of 5 months averaging 15-25 a minute (that was irritating!) even then, my doctors weren't concerned.
I agree that a monitor would be helpful to the doctors to see exactly what your heart is doing when you have the chest pain.
so you cant die from them
There are no absolute guarantees in life but odds are you will not die from them but something entirely unrelated to the heart. But do try to get your most concerning symptoms captured so you know for sure what you are dealing with.