hi
firstly i would like to say that im not a doctor,i am a nurse with 23 years experience in the job. I cant tell you what is wrong with you , i can only offer my opinion, and my opinion is that you dont have a tumour pressing on your heart or beleive me your symptoms would be much worse. it does sound to me like you could be suffering from GERD but you need to go see a doctor who can help you to get a proper diagnosis as you are obviously very anxious about this and anxiety can cause so many weird and painful symptoms on its own so please go see someone and put your mind at rest.
take care
Nell